1. Ribs and sternum. THORAX AS a WHOLE. Bones of upper limb (general data). Scapula, clavicle. HUMERUS, BONES OF THE FOREAM AND HAND
2. Bones of neurocranium (occipital, parietal, frontal bones)
3. Sphenoid and ethmoid
Lesson # 2
Theme 1 Ribs and sternum.THORAX AS WHOLE. Bones of upper limb (general data). Scapula, clavicle
In each rib we distinguish a bony part, the os costale, and at the anterior end the costal cartilage. There are twelve pairs of ribs, of which the upper seven are connected directly to the sternum and are called true ribs. The lower five ribs, false ribs, are joined indirectly (8th-l0th) or not at all (11th-12th) to the sternum. The 11 th and 12th rib can be contrasted with the others as floating ribs.
Each rib has a head, neck and a body.
The junction between the neck and the body is at the tubercle. The head and the tubercle each have an articular facet. From the 2nd to the
10th rib, the articular facet of the head
is divided into two by the crest of the
head of the rib. Lateral from the tubercle is the angle of the rib. With the exception of the
The 1st rib is small and flattened. On the inner circumference of its cranial surface is an area of roughness, the scalene tubercle. Posterior to it lies the sulcus of the subclavian artery, and in front of it is the sulcus of the subclavian vein. The 2nd rib has tuberosity for the serratus anterior muscle.
The ribs are elastic arches of bone, which form a large part of the thoracic skeleton. They are twelve in number on either side; but this number may be increased by the development of a cervical or lumbar rib, or may be diminished to eleven. The first seven are connected behind with the vertebral column, and in front, through the intervention of the costal cartilages, with the sternum ; they are called true or vertebro-sternal ribs. The remaining five are false ribs; of these, the first three have their cartilages attached to the cartilage of the rib above (vertebro-chondral): the last two are free at their anterior extremities and are termed floating or vertebral ribs. The ribs vary in their direction, the upper ones being less oblique than the lower; the obliquity reaches its maximum at the ninth rib, and gradually decreases from that rib to the twelfth. The ribs are situated one below the other in such a manner that spaces called intercostal spaces are left between them. The length of each space corresponds to that of the adjacent ribs and their cartilages; the breadth is greater in front than behind, and between the upper than the lower ribs. The ribs increase in length from the first to the seventh, below which they diminish to the twelfth. In breadth they decrease from above downward; in the upper ten the greatest breadth is at the sternal extremity.
Common Characteristics of the Ribs A rib from the middle of the series should be taken in order to study the common characteristics of these bones.
Each rib has two extremities, a posterior or vertebral, and an anterior or sternal, and an intervening portion—the body or shaft.
Posterior Extremity.—The posterior or vertebral extremity presents for examination a head, neck, and tubercle.
The head is marked by a kidney-shaped articular surface, divided by a horizontal crest into two facets for articulation with the depression formed on the bodies of two adjacent thoracic vertebr; the upper facet is the smaller; to the crest is attached the interarticular ligament.
The neck is the flattened portion which extends lateralward from the head; it is about
Body.—The body or shaft is thin and flat, with two surfaces, an external and an internal; and two borders, a superior and an inferior. The external surface is convex, smooth, and marked, a little in front of the tubercle, by a prominent line, directed downward and lateralward; this gives attachment to a tendon of the Iliocostalis, and is called the angle.
At this point the rib is bent in two directions, and at the same time twisted on its long axis. If the rib be laid upon its lower border, the portion of the body in front of the angle rests upon this border, while the portion behind the angle is bent medialward and at the same time tilted upward; as the result of the twisting, the external surface, behind the angle, looks downward, and in front of the angle, slightly upward. The distance between the angle and the tubercle is progressively greater from the second to the tenth ribs. The portion between the angle and the tubercle is rounded, rough, and irregular, and serves for the attachment of the Longissimus dorsi. The internal surface is concave, smooth, directed a little upward behind the angle, a little downward in front of it, and is marked by a ridge which commences at the lower extremity of the head; this ridge is strongly marked as far as the angle, and gradually becomes lost at the junction of the anterior and middle thirds of the bone. Between it and the inferior border is a groove, the costal groove, for the intercostal vessels and nerve. At the back part of the bone, this groove belongs to the inferior border, but just in front of the angle, where it is deepest and broadest, it is on the internal surface. The superior edge of the groove is rounded and serves for the attachment of an Intercostalis internus; the inferior edge corresponds to the lower margin of the rib, and gives attachment to an Intercostalis externus. Within the groove are seen the orifices of numerous small foramina for nutrient vessels which traverse the shaft obliquely from before backward. The superior border, thick and rounded, is marked by an external and an internal lip, more distinct behind than in front, which serve for the attachment of Intercostales externus and internus. The inferior border is thin, and has attached to it an Intercostalis externus.
Anterior Extremity.—The anterior or sternal extremity is flattened, and presents a porous, oval, concave depression, into which the costal cartilage is received.
Peculiar Ribs.—The first, second, tenth, eleventh, and twelfth ribs present certain variations from the common characteristics described above, and require special consideration.
First Rib.—The first rib is the most curved and usually the shortest of all the ribs; it is broad and flat, its surfaces looking upward and downward, and its borders inward and outward. The head is small, rounded, and possesses only a single articular facet, for articulation with the body of the first thoracic vertebra. The neck is narrow and rounded. The tubercle, thick and prominent, is placed on the outer border. There is no angle, but at the tubercle the rib is slightly bent, with the convexity upward, so that the head of the bone is directed downward. The upper surface of the body is marked by two shallow grooves, separated from each other by a slight ridge prolonged internally into a tubercle, the scalene tubercle, for the attachment of the Scalenus anterior; the anterior groove transmits the subclavian vein, the posterior the subclavian artery and the lowest trunk of the brachial plexus. 22 Behind the posterior groove is a rough area for the attachment of the Scalenus medius. The under surface is smooth, and destitute of a costal groove. The outer border is convex, thick, and rounded, and at its posterior part gives attachment to the first digitation of the Serratus anterior; the inner border is concave, thin, and sharp, and marked about its center by the scalene tubercle. The anterior extremity is larger and thicker than that of any of the other ribs.
Second Rib.—The second rib is much longer than the first, but has a very similar curvature. The non-articular portion of the tubercle is occasionally only feebly marked. The angle is slight, and situated close to the tubercle. The body is not twisted, so that both ends touch any plane surface upon which it may be laid; but there is a bend, with its convexity upward, similar to, though smaller than that found in the first rib. The body is not flattened horizontally like that of the first rib. Its external surface is convex, and looks upward and a little outward; near the middle of it is a rough eminence for the origin of the lower part of the first and the whole of the second digitation of the Serratus anterior; behind and above this is attached the Scalenus posterior. The internal surface, smooth, and concave, is directed downward and a little inward: on its posterior part there is a short costal groove.
Eleventh and Twelfth Ribs.—The eleventh and twelfth ribs have each a single articular facet on the head, which is of rather large size; they have no necks or tubercles, and are pointed at their anterior ends. The eleventh has a slight angle and a shallow costal groove. The twelfth has neither; it is much shorter than the eleventh, and its head is inclined slightly downward. Sometimes the twelfth rib is even shorter than the first.
Structure.—The ribs consist of highly vascular cancellous tissue, enclosed in a thin layer of compact bone.
Ossification.—Each rib, with the exception of the last two, is ossified from four centers; a primary center for the body, and three epiphysial centers, one for the head and one each for the articular and non-articular parts of the tubercle. The eleventh and twelfth ribs have each only two centers, those for the tubercles being wanting. Ossification begins near the angle toward the end of the second month of fetal life, and is seen first in the sixth and seventh ribs. The epiphyses for the head and tubercle make their appearance between the sixteenth and twentieth years, and are united to the body about the twenty-fifth year. Fawcett 23 states that “in all probability there is usually no epiphysis on the non-articular part of the tuberosity below the sixth or seventh rib.
Sternum (Breast Bone)
The sternum consists of the manubrium sterni, the body and the xiphoid process. Between the manubrium and the body lies the sternal angle. At the cranial end of the manubrium sterni is the jugular notch and lateral to it on either side the clavicular notches. The sternum has costal notches for a continuous cartilaginous joint with the I-VII ribs.
The sternum is an elongated, flattened bone, forming
the middle portion of the anterior wall of the thorax. Its upper end supports
the clavicles, and its margins articulate with the cartilages of the first
seven pairs of ribs. It consists of three parts, named from above
downward, the manubrium, the body or gladiolus, and the xiphoid
process; in early life the body consists of four segments or sternebrae. In its natural position the
inclination of the bone is oblique from above, downward and forward. It is
slightly convex in front and concave behind; broad above, becoming narrowed at
the point where the manubrium joins the body, after which it again widens a
little to below the middle of the body, and then narrows to its lower
extremity. Its average length in the adult is about
Manubrium (manubrium sterni).—The manubrium is of a somewhat quadrangular form, broad and thick above, narrow below at its junction with the body.
Surfaces.—Its anterior surface, convex from side to side, concave from above downward, is smooth, and affords attachment on either side to the sternal origins of the Pectoralis major and Sternocleidomastoideus. Sometimes the ridges limiting the attachments of these muscles are very distinct. Its posterior surface, concave and smooth, affords attachment on either side to the Sternohyoideus and Sternothyreoideus.
Lateral border of sternum
Borders.—The superior border is the thickest and presents at its center the jugular or presternal notch; on either side of the notch is an oval articular surface, directed upward, backward, and lateralward, for articulation with the sternal end of the clavicle. The inferior border, oval and rough, is covered in a fresh state with a thin layer of cartilage, for articulation with the body. The lateral borders are each marked above by a depression for the first costal cartilage, and below by a small facet, which, with a similar facet on the upper angle of the body, forms a notch for the reception of the costal cartilage of the second rib. Between the depression for the first costal cartilage and the demi-facet for the second is a narrow, curved edge, which slopes from above downward and medialward.
Body (corpus sterni; gladiolus).—The body, considerably longer, narrower, and thinner than the manubrium, attains its greatest breadth close to the lower end.
Surfaces.—Its anterior surface is nearly flat, directed upward and forward, and marked by three transverse ridges which cross the bone opposite the third, fourth, and fifth articular depressions. It affords attachment on either side to the sternal origin of the Pectoralis major. At the junction of the third and fourth pieces of the body is occasionally seen an orifice, the sternal foramen, of varying size and form. The posterior surface, slightly concave, is also marked by three transverse lines, less distinct, however, than those in front; from its lower part, on either side, the Transversus thoracis takes origin.
Borders.—The superior border is oval and articulates with the manubrium, the junction of the two forming the sternal angle (angulus Ludovici). The inferior border is narrow, and articulates with the xiphoid process. Each lateral border, at its superior angle, has a small facet, which with a similar facet on the manubrium, forms a cavity for the cartilage of the second rib; below this are four angular depressions which receive the cartilages of the third, fourth, fifth, and sixth ribs, while the inferior angle has a small facet, which, with a corresponding one on the xiphoid process, forms a notch for the cartilage of the seventh rib. These articular depressions are separated by a series of curved interarticular intervals, which diminish in length from above downward, and correspond to the intercostal spaces. Most of the cartilages belonging to the true ribs, as will be seen from the foregoing description, articulate with the sternum at the lines of junction of its primitive component segments. This is well seen in many of the lower animals, where the parts of the bone remain ununited longer than in man.
Xiphoid Process (processus xiphoideus; ensiform or xiphoid appendix).—The xiphoid process is the smallest of the three pieces: it is thin and elongated, cartilaginous in structure in youth, but more or less ossified at its upper part in the adult.
Surfaces.—Its anterior surface affords attachment on either side to the anterior costoxiphoid ligament and a small part of the Rectus abdominis; its posterior surface, to the posterior costoxiphoid ligament and to some of the fibers of the diaphragm and Transversus thoracis, its lateral borders, to the aponeuroses of the abdominal muscles. Above, it articulates with the lower end of the body, and on the front of each superior angle presents a facet for part of the cartilage of the seventh rib; below, by its pointed extremity, it gives attachment to the linea alba. The xiphoid process varies much in form; it may be broad and thin, pointed, bifid, perforated, curved, or deflected considerably to one or other side.
Structure.—The sternum is composed of highly vascular cancellous tissue, covered by a thin layer of compact bone which is thickest in the manubrium between the articular facets for the clavicles.
Ossification.—The sternum originally
consists of two cartilaginous bars, situated one on either side of the median
plane and connected with the cartilages of the upper nine ribs of its own side.
These two bars fuse with each other along the middle line to form the
cartilaginous sternum which is ossified from six centers:
one for the manubrium, four for the body, and one for the xiphoid process. The ossific centers appear in the
intervals between the articular depressions for the costal cartilages, in the
following order: in the manubrium and first piece of the body, during the sixth
month; in the second and third pieces of the body, during the seventh month of fetal life; in its fourth piece, during the first year
after birth; and in the xiphoid process, between the fifth and eighteenth
years. The centers make their appearance at the upper
parts of the segments, and proceed gradually downward. 20 To these may be added the occasional existence of two small episternal centers, which make
their appearance one on either side of the jugular notch; they are probably
vestiges of the episternal bone of the monotremata and lizards. Occasionally some of the segments
are formed from more than one center, the number and
position of which vary. Thus, the first piece may have two, three, or even six centers. When two are present, they are generally situated
one above the other, the upper being the larger; the second piece has seldom
more than one; the third, fourth, and fifth pieces are often formed from two centers placed laterally, the irregular union of which
explains the rare occurrence of the sternal foramen, or of the vertical fissure
which occasionally intersects this part of the bone constituting the
malformation known as fissura sterni; these conditions are further explained by the
manner in which the cartilaginous sternum is formed. More rarely still the
upper end of the sternum may be divided by a fissure.
Ossification of the sternum
Articulations.—The sternum articulates on either side with the clavicle and upper seven costal cartilages.
The skeleton of the thorax or chest is an osseo-cartilaginous cage, containing and protecting the principal organs of respiration and circulation. It is conical in shape, being narrow above and broad below, flattened from before backward, and longer behind than in front. It is somewhat reniform on transverse section on account of the projection of the vertebral bodies into the cavity.
The thorax from behind. (Spalteholz.)
Boundaries.—The posterior surface is formed by the twelve thoracic vertebr and the posterior parts of the ribs. It is convex from above downward, and presents on either side of the middle line a deep groove, in consequence of the lateral and backward direction which the ribs take from their vertebral extremities to their angles. The anterior surface, formed by the sternum and costal cartilages, is flattened or slightly convex, and inclined from above downward and forward. The lateral surfaces are convex; they are formed by the ribs, separated from each other by the intercostal spaces, eleven in number, which are occupied by the Intercostal muscles and membranes.
The upper opening of the thorax is reniform in shape, being broader from side to side than
from before backward. It is formed by the first thoracic vertebra behind, the
upper margin of the sternum in front, and the first rib on either side. It
slopes downward and forward, so that the anterior part of the opening is on a
lower level than the posterior. Its antero-posterior
diameter is about
The thorax from the right. (Spalteholz.)
The thorax of the female differs from that of the male as follows: 1. Its capacity is less. 2. The sternum is shorter. 3. The upper margin of the sternum is on a level with the lower part of the body of the third thoracic vertebra, whereas in the male it is on a level with the lower part of the body of the second. 4. The upper ribs are more movable, and so allow a greater enlargement of the upper part of the thorax.
Bones of the upper limb
In the upper limb we distinguish the shoulder girdle and the free extremity.
The shoulder girdle is formed by the scapulae and the clavicles.
Clavicle is an S-shaped bone. Toward the sternum is the sternal end with the sternal articular facet and toward the scapula the flat acromial end with acromial articular facet and between the two lies the body of the clavicle. Near the sternal end, on the lower surface of the clavicle, is the impression for the cosloclavicular ligament. The sulcus for the subclavian muscle lies on the undersurface of the clavicular body. The prominent conoid tubercle lies near the acromial end close to the trapezoid line.
The Bones of the Upper Extremity. 1. The Clavicle
(Ossa Extremitatis Superioris) & (Clavicula; Collar Bone)
The clavicleforms the anterior portion of the shoulder girdle. It is a long bone, curved somewhat like the italic letter f, and placed nearly horizontally at the upper and anterior part of the thorax, immediately above the first rib. It articulates medially with the manubrium sterni, and laterally with the acromion of the scapula. It presents a double curvature, the convexity being directed forward at the sternal end, and the concavity at the scapular end. Its lateral third is flattened from above downward, while its medial two-thirds is of a rounded or prismatic form.
Lateral Third.—The lateral third has two surfaces, an upper and a lower; and two borders, an anterior and a posterior.
Surface.—The upper surface is flat, rough, and marked by impressions for the attachments of the Deltoideus in front, and the Trapezius behind; between these impressions a small portion of the bone is subcutaneous. The under surface is flat. At its posterior border, near the point where the prismatic joins with the flattened portion, is a rough eminence, the coracoid tuberosity (conoid tubercle); this, in the natural position of the bone, surmounts the coracoid process of the scapula, and gives attachment to the conoid ligament. From this tuberosity an oblique ridge, the oblique or trapezoid ridge, runs forward and lateralward, and afford attachment to the trapezoid ligament.
Borders.—The anterior border is concave, thin, and rough, and gives attachment to the Deltoideus. The posterior border is convex, rough, thicker than the anterior, and gives attachment to the Trapezius.
Medial Two-thirds.—The medial two-thirds constitute the prismatic portion of the bone, which is curved so as to be convex in front, concave behind, and is marked by three borders, separating three surfaces.
Left clavicle. Superior surface.
Borders.—The anterior border is continuous with the anterior margin of the flat portion. Its lateral part is smooth, and corresponds to the interval between the attachments of the Pectoralis major and Deltoideus; its medial part forms the lower boundary of an elliptical surface for the attachment of the clavicular portion of the Pectoralis major, and approaches the posterior border of the bone. The superior border is continuous with the posterior margin of the flat portion, and separates the anterior from the posterior surface. Smooth and rounded laterally, it becomes rough toward the medial third for the attachment of the Sternocleidomastoideus, and ends at the upper angle of the sternal extremity. The posterior or subclavian border separates the posterior from the inferior surface, and extends from the coracoid tuberosity to the costal tuberosity; it forms the posterior boundary of the groove for the Subclavius, and gives attachment to a layer of cervical fascia which envelops the Omohyoideus.
Surfaces.—The anterior surface is
included between the superior and anterior borders. Its lateral part looks
upward, and is continuous with the superior surface of the flattened portion;
it is smooth, convex, and nearly subcutaneous, being covered only by the Platysma. Medially it is divided by a narrow subcutaneous
area into two parts: a lower, elliptical in form, and directed forward, for the
attachment of the Pectoralis major; and an upper for
the attachment of the Sternocleidomastoideus. The posterior
or cervical surface is smooth, and looks backward toward the root of the
neck. It is limited, above, by the superior border; below, by the subclavian border; medially, by the margin of the sternal
extremity; and laterally, by the coracoid tuberosity. It is concave medio-laterally, and is in relation, by its lower part,
with the transverse scapular vessels. This surface, at the junction of the
curves of the bone, is also in relation with the brachial plexus of nerves and
the subclavian vessels. It gives attachment, near the
sternal extremity, to part of the Sternohyoideus; and
presents, near the middle, an oblique foramen directed lateralward,
which transmits the chief nutrient artery of the bone. Sometimes there are two
foramina on the posterior surface, or one on the posterior and another on the
inferior surface. The inferior or subclavian
surface is bounded, in front, by the anterior border; behind, by the subclavian border. It is narrowed medially, but gradually
increases in width laterally, and is continuous with the under surface of the
flat portion. On its medial part is a broad rough surface, the costal
tuberosity (rhomboid impression), rather more than
The Sternal Extremity (extremitas sternalis; internal extremity).—The sternal extremity of the clavicle is triangular in form, directed medialward, and a little downward and forward; it presents an articular facet, concave from before backward, convex from above downward, which articulates with the manubrium sterni through the intervention of an articular disk. The lower part of the facet is continued on to the inferior surface of the bone as a small semi-oval area for articulation with the cartilage of the first rib. The circumference of the articular surface is rough, for the attachment of numerous ligaments; the upper angle gives attachment to the articular disk.
The Acromial Extremity (extremitas acromialis; outer extremity).—The acromial extremity presents a small, flattened, oval surface directed obliquely downward, for articulation with the acromion of the scapula. The circumference of the articular facet is rough, especially above, for the attachment of the acromioclavicular ligaments.
In the female, the clavicle is generally shorter, thinner, less curved, and smoother than in the male. In those persons who perform considerable manual labor it becomes thicker and more curved, and its ridges for muscular attachment are prominently marked.
Structure.—The clavicle consists of cancellous tissue, enveloped by a compact layer, which is much thicker in the intermediate part than at the extremities of the bone.
Ossification.—The clavicle begins to ossify before any other bone in the body; it is ossified from three centers—viz., two primary centers, a medial and a lateral, for the body, which appear during the fifth or sixth week of fetal life; and a secondary center for the sternal end, which appears about the eighteenth or twentieth year, and unites with the rest of the bone about the twenty-fifth year.
Scapula is a flat, triangular bone. It has a medial margin, a lateral margin and a superior margin, which are separated from each other by the superior and inferior angles and lateral angle. The anterior or costal surface is flat and slightly concave (subscapular fossa). It sometimes shows clear lines of muscle attachments. The dorsal surface is divided by the spine of the scapula into a smaller supraspinous fossa and a larger infraspinous fossa. The spine rises laterally to terminate in a flattened process, the acromion. Near the lateral end lies an oval articular facet for articulation with the clavicle.
The lateral angle bears the glenoid cavity with supraglenoid tubercle and the infraglenoid tubercle. The neck of the scapula is adjacent to the glenoid cavity.
The coracoid process lies above the glenoid cavity. On the upper margin of the scapula, lies the scapular notch.
(Shoulder Blade) the scapula forms the posterior part of the shoulder girdle. It is a flat, triangular bone, with two surfaces, three borders, and three angles.
Surfaces.—The costal or ventral surface presents a broad concavity, the subscapular fossa. The medial two-thirds of the fossa are marked by several oblique ridges, which run lateralward and upward. The ridges give attachment to the tendinous insertions, and the surfaces between them to the fleshy fibers, of the Subscapularis. The lateral third of the fossa is smooth and covered by the fibers of this muscle. The fossa is separated from the vertebral border by smooth triangular areas at the medial and inferior angles, and in the interval between these by a narrow ridge which is often deficient. These triangular areas and the intervening ridge afford attachment to the Serratus anterior. At the upper part of the fossa is a transverse depression, where the bone appears to be bent on itself along a line at right angles to and passing through the center of the glenoid cavity, forming a considerable angle, called the subscapular angle; this gives greater strength to the body of the bone by its arched form, while the summit of the arch serves to support the spine and acromion.
The dorsal surface is arched from above downward, and is subdivided into two unequal parts by the spine; the portion above the spine is called the supraspinatous fossa, and that below it the infraspinatous fossa.
The supraspinatous fossa, the smaller of the two, is concave, smooth, and broader at its vertebral than at its humeral end; its medial two-thirds give origin to the Supraspinatus.
The infraspinatous fossa is much larger than the preceding; toward its vertebral margin a shallow concavity is seen at its upper part; its center presents a prominent convexity, while near the axillary border is a deep groove which runs from the upper toward the lower part. The medial two-thirds of the fossa give origin to the Infraspinatus; the lateral third is covered by this muscle.
The dorsal surface is marked near the axillary border by an elevated
ridge, which runs from the lower part of the glenoid
cavity, downward and backward to the vertebral border, about
The Spine (spina scapul).—The spine is a prominent plate of bone, which crosses obliquely the medial four-fifths of the dorsal surface of the scapula at its upper part, and separates the supra- from the infraspinatous fossa. It begins at the vertical border by a smooth, triangular area over which the tendon of insertion of the lower part of the Trapezius glides, and, gradually becoming more elevated, ends in the acromion, which overhangs the shoulder-joint. The spine is triangular, and flattened from above downward, its apex being directed toward the vertebral border. It presents two surfaces and three borders. Its superior surface is concave; it assits in forming the supraspinatous fossa, and gives origin to part of the Supraspinatus. Its inferior surface forms part of the infraspinatous fossa, gives origin to a portion of the Infraspinatus, and presents near its center the orifice of a nutrient canal. Of the three borders, the anterior is attached to the dorsal surface of the bone; the posterior, or crest of the spine, is broad, and presents two lips and an intervening rough interval. The Trapezius is attached to the superior lip, and a rough tubercle is generally seen on that portion of the spine which receives the tendon of insertion of the lower part of this muscle. The Deltoideus is attached to the whole length of the inferior lip. The interval between the lips is subcutaneous and partly covered by the tendinous fibers of these muscles. The lateral border, or base, the shortest of the three, is slightly concave; its edge, thick and round, is continuous above with the under surface of the acromion, below with the neck of the scapula. It forms the medial boundary of the great scapular notch, which serves to connect the supra- and infraspinatous foss.
The Acromion.—The acromion forms the summit of the shoulder, and is a large, somewhat triangular or oblong process, flattened from behind forward, projecting at first lateralward, and then curving forward and upward, so as to overhang the glenoid cavity. Its superior surface, directed upward, backward, and lateralward, is convex, rough, and gives attachment to some fibers of the Deltoideus, and in the rest of its extent is subcutaneous. Its inferior surface is smooth and concave. Its lateral border is thick and irregular, and presents three or four tubercles for the tendinous origins of the Deltoideus. Its medial border, shorter than the lateral, is concave, gives attachment to a portion of the Trapezius, and presents about its center a small, oval surface for articulation with the acromial end of the clavicle.
Its apex, which corresponds to the point of meeting of these two borders in front, is thin, and has attached to it the coracoacromial ligament.
Left scapula. Dorsal surface.
Borders.—Of the three borders of the
scapula, the superior is the shortest and thinnest; it is concave, and
extends from the medial angle to the base of the coracoid process. At its
lateral part is a deep, semicircular notch, the scapular
notch, formed partly by the base of the coracoid process. This notch is
converted into a foramen by the superior transverse ligament, and serves for
the passage of the suprascapular nerve; sometimes the
ligament is ossified. The adjacent part of the superior border affords
attachment to the Omohyoideus. The axillary border
is the thickest of the three. It begins above at the lower margin of the glenoid cavity, and inclines obliquely downward and
backward to the inferior angle. Immediately below the glenoid
cavity is a rough impression, the infraglenoid
Posterior view of the thorax and shoulder girdle.
Angles.—Of the three angles, the medial, formed by the junction of the superior and vertebral borders, is thin, smooth, rounded, inclined somewhat lateralward, and gives attachment to a few fibers of the Levator scapul. The inferior angle, thick and rough, is formed by the union of the vertebral and axillary borders; its dorsal surface affords attachment to the Teres major and frequently to a few fibers of the Latissimus dorsi. The lateral angle is the thickest part of the bone, and is sometimes called the head of the scapula. On it is a shallow pyriform, articular surface, the glenoid cavity, which is directed lateralward and forward and articulates with the head of the humerus; it is broader below than above and its vertical diameter is the longest. The surface is covered with cartilage in the fresh state; and its margins, slightly raised, give attachment to a fibrocartilaginous structure, the glenoidal labrum, which deepens the cavity. At its apex is a slight elevation, the supraglenoid tuberosity, to which the long head of the Biceps brachii is attached. The neck of the scapula is the slightly constricted portion which surrounds the head; it is more distinct below and behind than above and in front.
The Coracoid Process (processus coracoideus).—The coracoid process is a thick curved process attached by a broad base to the upper part of the neck of the scapula; it runs at first upward and medialward; then, becoming smaller, it changes its direction, and projects forward and lateralward. The ascending portion, flattened from before backward, presents in front a smooth concave surface, across which the Subscapularis passes. The horizontal portion is flattened from above downward; its upper surface is convex and irregular, and gives attachment to the Pectoralis minor; its under surface is smooth; its medial and lateral borders are rough; the former gives attachment to the Pectoralis minor and the latter to the coracoacromial ligament; the apex is embraced by the conjoined tendon of origin of the Coracobrachialis and short head of the Biceps brachii and gives attachment to the coracoclavicular fascia. On the medial part of the root of the coracoid process is a rough impression for the attachment of the conoid ligament; and running from it obliquely forward and lateralward, on to the upper surface of the horizontal portion, is an elevated ridge for the attachment of the trapezoid ligament.
Left scapula. Lateral view.
Structure.—The head, processes, and the thickened parts of the bone, contain cancellous tissue; the rest consists of a thin layer of compact tissue. The central part of the supraspinatous fossa and the upper part of the infraspinatous fossa, but especially the former, are usually so thin as to be semitransparent; occasionally the bone is found wanting in this situation, and the adjacent muscles are separated only by fibrous tissue.
Ossification—The scapula is ossified from seven or more centers: one for the body, two for the coracoid process, two for the acromion, one for the vertebral border, and one for the inferior angle.
Ossification of the body begins about the second month of fetal life, by the formation of an irregular quadrilateral plate of bone, immediately behind the glenoid cavity. This plate extends so as to form the chief part of the bone, the spine growing up from its dorsal surface about the third month. At birth, a large part of the scapula is osseous, but the glenoid cavity, the coracoid process, the acromion, the vertebral border, and the inferior angle are cartilaginous. From the fifteenth to the eighteenth month after birth, ossification takes place in the middle of the coracoid process, which as a rule becomes joined with the rest of the bone about the fifteenth year. Between the fourteenth and twentieth years, ossification of the remaining parts takes place in quick succession, and usually in the following order; first, in the root of the coracoid process, in the form of a broad scale; secondly, near the base of the acromion; thirdly, in the inferior angle and contiguous part of the vertebral border; fourthly, near the extremity of the acromion; fifthly, in the vertebral border. The base of the acromion is formed by an extension from the spine; the two separate nuclei of the acromion unite, and then join with the extension from the spine. The upper third of the glenoid cavity is ossified from a separate center (subcoracoid), which makes its appearance between the tenth and eleventh years and joins between the sixteenth and the eighteenth. Further, an epiphysical plate appears for the lower part of the glenoid cavity, while the tip of the coracoid process frequently presents a separate nucleus. These various epiphyses are joined to the bone by the twenty-fifth year. Failure of bony union between the acromion and spine sometimes occurs, the junction being effected by fibrous tissue, or by an imperfect articulation; in some cases of supposed fracture of the acromion with ligamentous union, it is probable that the detached segment was never united to the rest of the bone.
Plan of ossification of the scapula. From seven centers
HUMERUS, BONES OF THE FOREAM AND HAND
The bones of the free upper limb
The bones of the free upper limb are the skeleton of arm, forearm and hand.
Humerus articulates with the scapula and the radius and ulna. It consists of the body and upper (proximal) and lower (distal) ends.
The proximal end is formed by the head of the humerus, adjoining the anatomic neck. There are the greater tubercle, and medially is the lesser tubercle. Between these tubercles begins the intertubercular sulcus, which is bounded distally by the crests of the lesser and greater tubercles. The surgical neck lies proximally on the body of the humerus. In the middle of the body lies laterally the deltoid tuberosity and sulcus for the radial nerve. The body may be divided into an anteromedial surface with a medial border, and an anterotateral surface with a lateral border, which becomes sharpened distally and is called the lateral supracondylar crisla. The distal end of the humerus bears on its medial side the large medial epicondyle and on the lateral side the smaller lateral epicondyle.
The trochlea and the capitulum of the humerus form the humeral condyles for articulation with the bones of the forearm. The radial fossa lies proximal to the capitulum and proximal to the trochlea is the somewhat larger coronoid fossa.
Medial to the trochlea there is a shallow groove, the sulcus for the ulnar nerve. On the posterior surface above the trochlea is a deep pit, the olecranon fossa.
The ulna has a shaft and proximal and distal ends. The proximal end bears a hook-like process, the olecranon. Anteriorly the trochlear notch extends as far as the coronoid process, and laterally is the radial notch into which the articular circumference of the radius fits. At the junction with the shaft lies the ulnar tuberosity. Laterally lies radial notch. The interosseous border lies laterally. The anterior surface is separated from the medial surface by the anterior border. The latter in turn is separated from the posterior surface by the posterior margin. In the middle of the ulna, on its anterior surface, is the nutrient foramen. The articular circumference is on the head of the ulna. At the distal end of the ulna is the small styloid process.
The radius consists of a shaft and proximal and distal ends. At the proximal end is the head of the radius with the fovea articularis, which is continuous with the articular circumference. On the medial side of the transition between the neck of the radius and the shaft has the radial tuberosity. The shaft has a medially facing interosseous border, an anterior surface, and anterior border, a lateral surface and a posterior border, which forms the boundary between the lateral and the posterior surfaces. At the lower end of the radius lies the styloid process and medial to it is the ulnar notch. The carpal articular surface faces distally.
Bones of the hand consist of carpus, metacarpus and digits.
The carpus consists of eight carpal bones arranged in two rows of four. In the proximal rowfrom lateral to medial are the scaphoid, lunate, triquetrum and pisiform. In the distal row from the lateral to the medial side are the trapezium, trapezoid, capitate and hamate.
The five metacarpals of the hand each have a head, a body and a base. On all of the there are articular facets at one end (base) for articulation with the carpals and at the other (head) for the phalanges.
Each digit consists of bones namely a proximal, a medial and a distal phalanx. The sole exception is the thumb, which has only two phalanges. At the distal end halanx there is the tuberosity of the distal phalanx.
Theme 2 Bones of neurocranium
(occipital, parietal, frontal bones)
Bones of skull
Bones of skull divide into neurocranium and viscerocranium bones.
Neurocranium bones form the base and the roof.
Base of the skull has an inner and outer surfaces. It is formed by frontal, ethmoid, sphenoid temporal and occipital bones. Inner base consists of anterior, middle and posterior cranial fossae. Roof of the skull is formed by occipital, parietal, temporal and frontal bones.
Occipital bone consists of occipital squama, lateral and basilar parts.
Squama is situated above and behind the foramen magnum and possesses external occipital protuberance and external crest on outer surface and it. Also there are the superior and inferior nuchal lines. The internal surface is deeply concave and carries a crucial eminence. At the point of intersection of the four divisions of the crucial eminence and internal occipital protuberance. Right and left sides of them is a deep groove, the superior sagittal sulcus, lower there is the internal occipital crest.
Lateral Parts (pars lateralis) are situated at the sides of the foramen magnum; on their under surfaces are the condyles with and the hypoglossal canal. Behind either condyle is the condyloid fossa. Laterally is the jugular process, excavated in front by the jugular notch. Basilar Part (pars basilaris) extends forward and upward from the foramen magnum and form the back part of the clivus. On its lower surface is the pharyngeal tubercle which gives attachment to the fibrous raphe of the pharynx.
The Parietal Bone (Os Parietale) form, by their union, the sides and roof of the cranium. Each bone is irregularly quadrilateral in form and has convex external (with tuber parietale) surface and concave internal surfaces. Bone has four corners: frontal, sphenoid, mastoid and occipital; and four margins. Near the sagittal margin are several depressions for the arachnoid granulation.
The Frontal Bone (Os Frontale) consists of three portions — the squama, and an orbital and nasal portions, which enters into the formation of the roofs of the orbital and nasal cavities. Squama in the external surface has tuber frontale and the superciliary arches; are joined to one another by a smooth elevation named the glabella. At the supraorbital margin is a notch, sometimes converted into a foramen. The supraorbital margin ends laterally in the zygomatic process. Nasal part presents the ethmoid notch and a sharp spine. In nasal part they can find aperture for frontal sinus.
The internal surface of the squama is concave and contains the superior sagittal sulcus and the frontal crest. The crest ends below in a small notch which is converted into a foramen, the foramen cecum. Orbital part presents the lacrimal gland fossa and the fovea trochlearis with trochlear spine.
(Os Frontale)The frontal bone resembles a cockle-shell in form, and consists of two portions—a vertical portion, the squama, corresponding with the region of the forehead; and an orbital or horizontal portion, which enters into the formation of the roofs of the orbital and nasal cavities.
frontalis).—Surfaces.—The external surface
of this portion is convex and usually exhibits, in the lower part of the middle
line, the remains of the frontal or metopic suture; in infancy
this suture divides the bone into two, a condition which may persist throughout
life. On either side of this suture, about
Frontal bone. Outer surface.
The internal surface of the squama is concave and presents in the upper part of the middle line a vertical groove, the sagittal sulcus, the edges of which unite below to form a ridge, the frontal crest; the sulcus lodges the superior sagittal sinus, while its margins and the crest afford attachment to the falx cerebri. The crest ends below in a small notch which is converted into a foramen, the foramen cecum, by articulation with the ethmoid. This foramen varies in size in different subjects, and is frequently impervious; when open, it transmits a vein from the nose to the superior sagittal sinus. On either side of the middle line the bone presents depressions for the convolutions of the brain, and numerous small furrows for the anterior branches of the middle meningeal vessels. Several small, irregular foss may also be seen on either side of the sagittal sulcus, for the reception of the arachnoid granulations.
Orbital or Horizontal Part (pars orbitalis).—This portion consists of two thin triangular plates, the orbital plates, which form the vaults of the orbits, and are separated from one another by a median gap, the ethmoidal notch.
Surfaces.—The inferior surface of each orbital plate is smooth and concave, and presents, laterally, under cover of the zygomatic process, a shallow depression, the lacrimal fossa, for the lacrimal gland; near the nasal part is a depression, the fovea trochlearis, or occasionally a small trochlear spine, for the attachment of the cartilaginous pulley of the Obliquus oculi superior. The superior surface is convex, and marked by depressions for the convolutions of the frontal lobes of the brain, and faint grooves for the meningeal branches of the ethmoidal vessels.
The ethmoidal notch separates the two orbital plates; it is quadrilateral, and filled, in the articulated skull, by the cribriform plate of the ethmoid. The margins of the notch present several half-cells which, when united with corresponding half-cells on the upper surface of the ethmoid, complete the ethmoidal air cells. Two grooves cross these edges transversely; they are converted into the anterior and posterior ethmoidal canals by the ethmoid, and open on the medial wall of the orbit. The anterior canal transmits the nasociliary nerve and anterior ethmoidal vessels, the posterior, the posterior ethmoidal nerve and vessels. In front of the ethmoidal notch, on either side of the frontal spine, are the openings of the frontal air sinuses. These are two irregular cavities, which extend backward, upward, and lateralward for a variable distance between the two tables of the skull; they are separated from one another by a thin bony septum, which often deviates to one or other side, with the result that the sinuses are rarely symmetrical. Absent at birth, they are usually fairly well-developed between the seventh and eighth years, but only reach their full size after puberty. They vary in size in different persons, and are larger in men than in women. They are lined by mucous membrane, and each communicates with the corresponding nasal cavity by means of a passage called the frontonasal duct.
Borders.—The border of the squama is thick, strongly serrated, bevelled at the expense of the inner table above, where it rests upon the parietal bones, and at the expense of the outer table on either side, where it receives the lateral pressure of those bones; this border is continued below into a triangular, rough surface, which articulates with the great wing of the sphenoid. The posterior borders of the orbital plates are thin and serrated, and articulate with the small wings of the sphenoid.
Structure.—The squama and the zygomatic processes are very thick, consisting of diploic tissue contained between two compact lamin; the diploic tissue is absent in the regions occupied by the frontal air sinuses. The orbital portion is thin, translucent, and composed entirely of compact bone; hence the facility with which instruments can penetrate the cranium through this part of the orbit; when the frontal sinuses are exceptionally large they may extend backward for a considerable distance into the orbital portion, which in such cases also consists of only two tables.
Ossification—The frontal bone is ossified in membrane from two primary centers, one for each half, which appear toward the end of the second month of fetal life, one above each supraorbital margin. From each of these centers ossification extends upward to form the corresponding half of the squama, and backward to form the orbital plate. The spine is ossified from a pair of secondary centers, on either side of the middle line; similar centers appear in the nasal part and zygomatic processes. At birth the bone consists of two pieces, separated by the frontal suture, which is usually obliterated, except at its lower part, by the eighth year, but occasionally persists throughout life. It is generally maintained that the development of the frontal sinuses begins at the end of the first or beginning of the second year, but Onodi’s researches indicate that development begins at birth. The sinuses are of considerable size by the seventh or eighth year, but do not attain their full proportions until after puberty.
Articulations.—The frontal articulates with twelve bones: the sphenoid, the ethmoid, the two parietals, the two nasals, the two maxill, the two lacrimals, and the two zygomatics.
Theme 3 Sphenoid and ethmoid bones
The Sphenoid Bone (Os Sphenoidale) is situated at the base of the skull and is divided into a body, two great and two small wings and two pterygoid processes.
Body (corpus sphenoidale) contain the sphenoidal air sinuses. Superiorly there is chiasmatic groove and tuberculum sellae forward from the sella turcica with the hypophiseal fossa and dorsum sellae. Behind the dorsum sellae is the clivus.
The anterior surface of the body presents the sphenoidal crestthat continuis into rostrum.
The Great Wings (alae major) have the cerebral surface with the foramen rotundum, foramen ovale and foramen spinosum. Also they differ maxillar, temporal (with the infratemporal crest) and orbital surfaces.
The Small Wings (alae minor) arise from the upper and anterior parts of the body. Between the two roots is the optic canal. Alae minor borders the superior orbital fissure with alae major.
Pterygoid Processes (processus pterygoidei) descend perpendicularly from the regions where the body and great wings unite. Each process consists of a medial and a lateral plate, the upper parts of which are fused anteriorly; a vertical sulcus, the pterygopalatine groove. The plates are separated below by the pterygoid incisura. The two plates diverge behind and enclose between them a V-shaped fossa, the pterygoid fossa. Pterygoid canal is in base of process. The medial pterygoid plate has the pterygoid hamulus.
The sphenoid bone is situated at the base of the skull in front of the temporals and basilar part of the occipital. It somewhat resembles a bat with its wings extended, and is divided into a median portion or body, two great and two small wings extending outward from the sides of the body, and two pterygoid processes which project from it below.
Body (corpus sphenoidale).—The body, more or less cubical in shape, is hollowed out in its interior to form two large cavities, the sphenoidal air sinuses, which are separated from each other by a septum.
Surfaces.—The superior surface of the body presents in front a prominent spine, the ethmoidal spine, for articulation with the cribriform plate of the ethmoid; behind this is a smooth surface slightly raised in the middle line, and grooved on either side for the olfactory lobes of the brain. This surface is bounded behind by a ridge, which forms the anterior border of a narrow, transverse groove, the chiasmatic groove (optic groove), above and behind which lies the optic chiasma; the groove ends on either side in the optic foramen, which transmits the optic nerve and ophthalmic artery into the orbital cavity. Behind the chiasmatic groove is an elevation, the tuberculum sell; and still more posteriorly, a deep depression, the sella turcica, the deepest part of which lodges the hypophysis cerebri and is known as the fossa hypophyseos. The anterior boundary of the sella turcica is completed by two small eminences, one on either side, called the middle clinoid processes, while the posterior boundary is formed by a square-shaped plate of bone, the dorsum sell, ending at its superior angles in two tubercles, the posterior clinoid processes, the size and form of which vary considerably in different individuals. The posterior clinoid processes deepen the sella turcica, and give attachment to the tentorium cerebelli. On either side of the dorsum sell is a notch for the passage of the abducent nerve, and below the notch a sharp process, the petrosal process, which articulates with the apex of the petrous portion of the temporal bone, and forms the medial boundary of the foramen lacerum. Behind the dorsum sell is a shallow depression, the clivus, which slopes obliquely backward, and is continuous with the groove on the basilar portion of the occipital bone; it supports the upper part of the pons.
Sphenoid bone. Anterior and inferior surfaces.
The lateral surfaces of the body are united with the great wings and the medial pterygoid plates. Above the attachment of each great wing is a broad groove, curved something like the italic letter f; it lodges the internal carotid artery and the cavernous sinus, and is named the carotid groove. Along the posterior part of the lateral margin of this groove, in the angle between the body and great wing, is a ridge of bone, called the lingula.
The posterior surface, quadrilateral in form is joined, during infancy and adolescence, to the basilar part of the occipital bone by a plate of cartilage. Between the eighteenth and twenty-fifth years this becomes ossified, ossification commencing above and extending downward.
The anterior surface of the body presents, in the middle line, a vertical crest, the sphenoidal crest, which articulates with the perpendicular plate of the ethmoid, and forms part of the septum of the nose. On either side of the crest is an irregular opening leading into the corresponding sphenoidal air sinus. These sinuses are two large, irregular cavities hollowed out of the interior of the body of the bone, and separated from one another by a bony septum, which is commonly bent to one or the other side. They vary considerably in form and size, 30 are seldom symmetrical, and are often partially subdivided by irregular bony lamin. Occasionally, they extend into the basilar part of the occipital nearly as far as the foramen magnum. They begin to be developed before birth, and are of a considerable size by the age of six. They are partially closed, in front and below, by two thin, curved plates of bone, the sphenoidal conch, leaving in the articulated skull a round opening at the upper part of each sinus by which it communicates with the upper and back part of the nasal cavity and occasionally with the posterior ethmoidal air cells. The lateral margin of the anterior surface is serrated, and articulates with the lamina papyracea of the ethmoid, completing the posterior ethmoidal cells; the lower margin articulates with the orbital process of the palatine bone, and the upper with the orbital plate of the frontal bone.
Sphenoid bone. Upper and posterior surfaces
The inferior surface presents, in the middle line, a triangular spine, the sphenoidal rostrum, which is continuous with the sphenoidal crest on the anterior surface, and is received in a deep fissure between the al of the vomer. On either side of the rostrum is a projecting lamina, the vaginal process, directed medialward from the base of the medial pterygoid plate, with which it will be described.
The Great Wings (al magn).—The great wings, or ali-sphenoids, are two strong processes of bone, which arise from the sides of the body, and are curved upward, lateralward, and backward; the posterior part of each projects as a triangular process which fits into the angle between the squama and the petrous portion of the temporal and presents at its apex a downwardly directed process, the spina angularis (sphenoidal spine).
Surfaces.—The superior or cerebral surface of each great wing forms part of the middle fossa of the skull; it is deeply concave, and presents depressions for the convolutions of the temporal lobe of the brain. At its anterior and medial part is a circular aperture, the foramen rotundum, for the transmission of the maxillary nerve. Behind and lateral to this is the foramen ovale, for the transmission of the mandibular nerve, the accessory meningeal artery, and sometimes the lesser superficial petrosal nerve. 31 Medial to the foramen ovale, a small aperture, the foramen Vesalii, may occasionally be seen opposite the root of the pterygoid process; it opens below near the scaphoid fossa, and transmits a small vein from the cavernous sinus. Lastly, in the posterior angle, near to and in front of the spine, is a short canal, sometimes double, the foramen spinosum, which transmits the middle meningeal vessels and a recurrent branch from the mandibular nerve.
The lateral surface is convex, and divided by a transverse ridge, the infratemporal crest, into two portions. The superior or temporal portion, convex from above downward, concave from before backward, forms a part of the temporal fossa, and gives attachment to the Temporalis; the inferior or infratemporal, smaller in size and concave, enters into the formation of the infratemporal fossa, and, together with the infratemporal crest, affords attachment to the Pterygoideus externus. It is pierced by the foramen ovale and foramen spinosum, and at its posterior part is the spina angularis, which is frequently grooved on its medial surface for the chorda tympani nerve. To the spina angularis are attached the sphenomandibular ligament and the Tensor veli palatini. Medial to the anterior extremity of the infratemporal crest is a triangular process which serves to increase the attachment of the Pterygoideus externus; extending downward and medialward from this process on to the front part of the lateral pterygoid plate is a ridge which forms the anterior limit of the infratemporal surface, and, in the articulated skull, the posterior boundary of the pterygomaxillary fissure.
The orbital surface of the great wing smooth, and quadrilateral in shape, is directed forward and medialward and forms the posterior part of the lateral wall of the orbit. Its upper serrated edge articulates with the orbital plate of the frontal. Its inferior rounded border forms the postero-lateral boundary of the inferior orbital fissure. Its medial sharp margin forms the lower boundary of the superior orbital fissure and has projecting from about its center a little tubercle which gives attachment to the inferior head of the Rectus lateralis oculi; at the upper part of this margin is a notch for the transmission of a recurrent branch of the lacrimal artery. Its lateral margin is serrated and articulates with the zygomatic bone. Below the medial end of the superior orbital fissure is a grooved surface, which forms the posterior wall of the pterygopalatine fossa, and is pierced by the foramen rotundum.
Margin—Commencing from behind, that portion of the circumference of the great wing which extends from the body to the spine is irregular. Its medial half forms the anterior boundary of the foramen lacerum, and presents the posterior aperture of the pterygoid canal for the passage of the corresponding nerve and artery. Its lateral half articulates, by means of a synchondrosis, with the petrous portion of the temporal, and between the two bones on the under surface of the skull, is a furrow, the sulcus tub, for the lodgement of the cartilaginous part of the auditory tube. In front of the spine the circumference presents a concave, serrated edge, bevelled at the expense of the inner table below, and of the outer table above, for articulation with the temporal squama. At the tip of the great wing is a triangular portion, bevelled at the expense of the internal surface, for articulation with the sphenoidal angle of the parietal bone; this region is named the pterion. Medial to this is a triangular, serrated surface, for articulation with the frontal bone; this surface is continuous medially with the sharp edge, which forms the lower boundary of the superior orbital fissure, and laterally with the serrated margin for articulation with the zygomatic bone.
The Small Wings (al parv).—The small wings or orbito-sphenoids are two thin triangular plates, which arise from the upper and anterior parts of the body, and, projecting lateralward, end in sharp points
Surfaces.—The superior surface of each is flat, and supports part of the frontal lobe of the brain. The inferior surface forms the back part of the roof of the orbit, and the upper boundary of the superior orbital fissure. This fissure is of a triangular form, and leads from the cavity of the cranium into that of the orbit: it is bounded medially by the body; above, by the small wing; below, by the medial margin of the orbital surface of the great wing; and is completed laterally by the frontal bone. It transmits the oculomotor, trochlear, and abducent nerves, the three branches of the ophthalmic division of the trigeminal nerve, some filaments from the cavernous plexus of the sympathetic, the orbital branch of the middle meningeal artery, a recurrent branch from the lacrimal artery to the dura mater, and the ophthalmic vein.
Borders.—The anterior border is serrated for articulation with the frontal bone. The posterior border, smooth and rounded, is received into the lateral fissure of the brain; the medial end of this border forms the anterior clinoid process, which gives attachment to the tentorium cerebelli; it is sometimes joined to the middle clinoid process by a spicule of bone, and when this occurs the termination of the groove for the internal carotid artery is converted into a foramen (carotico-clinoid). The small wing is connected to the body by two roots, the upper thin and flat, the lower thick and triangular; between the two roots is the optic foramen, for the transmission of the optic nerve and ophthalmic artery.
Pterygoid Processes (processus pterygoidei).—The pterygoid processes, one on either side, descend perpendicularly from the regions where the body and great wings unite. Each process consists of a medial and a lateral plate, the upper parts of which are fused anteriorly; a vertical sulcus, the pterygopalatine groove, descends on the front of the line of fusion. The plates are separated below by an angular cleft, the pterygoid fissure, the margins of which are rough for articulation with the pyramidal process of the palatine bone. The two plates diverge behind and enclose between them a V-shaped fossa, the pterygoid fossa, which contains the Pterygoideus internus and Tensor veli palatini. Above this fossa is a small, oval, shallow depression, the scaphoid fossa, which gives origin to the Tensor veli palatini. The anterior surface of the pterygoid process is broad and triangular near its root, where it forms the posterior wall of the pterygopalatine fossa and presents the anterior orifice of the pterygoid canal.
Lateral Pterygoid Plate.—The lateral pterygoid plate is broad, thin, and everted; its lateral surface forms part of the medial wall of the infratemporal fossa, and gives attachment to the Pterygoideus externus; its medial surface forms part of the pterygoid fossa, and gives attachment to the Pterygoideus internus.
Medial Pterygoid Plate.—The medial pterygoid plate is narrower and longer than the lateral; it curves lateralward at its lower extremity into a hook-like process, the pterygoid hamulus, around which the tendon of the Tensor veli palatini glides. The lateral surface of this plate forms part of the pterygoid fossa, the medial surface constitutes the lateral boundary of the choana or posterior aperture of the corresponding nasal cavity. Superiorly the medial plate is prolonged on to the under surface of the body as a thin lamina, named the vaginal process, which articulates in front with the sphenoidal process of the palatine and behind this with the ala of the vomer. The angular prominence between the posterior margin of the vaginal process and the medial border of the scaphoid fossa is named the pterygoid tubercle, and immediately above this is the posterior opening of the pterygoid canal. On the under surface of the vaginal process is a furrow, which is converted into a canal by the sphenoidal process of the palatine bone, for the transmission of the pharyngeal branch of the internal maxillary artery and the pharyngeal nerve from the sphenopalatine ganglion. The pharyngeal aponeurosis is attached to the entire length of the posterior edge of the medial plate, and the Constrictor pharyngis superior takes origin from its lower third. Projecting backward from near the middle of the posterior edge of this plate is an angular process, the processus tubarius, which supports the pharyngeal end of the auditory tube. The anterior margin of the plate articulates with the posterior border of the vertical part of the palatine bone.
The Sphenoidal Conch (conch sphenoidales; sphenoidal turbinated processes).—The sphenoidal conch are two thin, curved plates, situated at the anterior and lower part of the body of the sphenoid. An aperture of variable size exists in the anterior wall of each, and through this the sphenoidal sinus opens into the nasal cavity. Each is irregular in form, and tapers to a point behind, being broader and thinner in front. Its upper surface is concave, and looks toward the cavity of the sinus; its under surface is convex, and forms part of the roof of the corresponding nasal cavity. Each bone articulates in front with the ethmoid, laterally with the palatine; its pointed posterior extremity is placed above the vomer, and is received between the root of the pterygoid process laterally and the rostrum of the sphenoid medially. A small portion of the sphenoidal concha sometimes enters into the formation of the medial wall of the orbit, between the lamina papyracea of the ethmoid in front, the orbital plate of the palatine below, and the frontal bone above.
Ossification.—Until the seventh or eighth month of fetal life the body of the sphenoid consists of two parts, viz., one in front of the tuberculum sell, the presphenoid, with which the small wings are continuous; the other, comprising the sella turcica and dorsum sell, the postsphenoid, with which are associated the great wings, and pterygoid processes. The greater part of the bone is ossified in cartilage. There are fourteen centers in all, six for the presphenoid and eight for the postsphenoid.
Sphenoid bone at birth. Posterior aspect.
Presphenoid.—About the ninth week of fetal life an ossific center appears for each of the small wings (orbitosphenoids) just lateral to the optic foramen; shortly afterward two nuclei appear in the presphenoid part of the body. The sphenoidal conch are each developed from a center which makes its appearance about the fifth month; 32 at birth they consist of small triangular lamin, and it is not until the third year that they become hollowed out and coneshaped; about the fourth year they fuse with the labyrinths of the ethmoid, and between the ninth and twelfth years they unite with the sphenoid.
Postsphenoid.—The first ossific nuclei are those for the great wings (ali-sphenoids) 33. One makes its appearance in each wing between the foramen rotundum and foramen ovale about the eighth week. The orbital plate and that part of the sphenoid which is found in the temporal fossa, as well as the lateral pterygoid plate, are ossified in membrane (Fawcett) 34. Soon after, the centers for the postsphenoid part of the body appear, one on either side of the sella turcica, and become blended together about the middle of fetal life. Each medial pterygoid plate (with the exception of its hamulus) is ossified in membrane, and its center probably appears about the ninth or tenth week; the hamulus becomes chondrified during the third month, and almost at once undergoes ossification (Fawcett). 35 The medial joins the lateral pterygoid plate about the sixth month. About the fourth month a center appears for each lingula and speedily joins the rest of the bone.
The presphenoid is united to the postsphenoid about the eighth month, and at birth the bone is in three pieces a central, consisting of the body and small wings, and two lateral, each comprising a great wing and pterygoid process. In the first year after birth the great wings and body unite, and the small wings extend inward above the anterior part of the body, and, meeting with each other in the middle line, form an elevated smooth surface, termed the jugum sphenoidale. By the twenty-fifth year the sphenoid and occipital are completely fused. Between the pre- and postsphenoid there are occasionally seen the remains of a canal, the canalis cranio-pharyngeus, through which, in early fetal life, the hypophyseal diverticulum of the buccal ectoderm is transmitted.
The sphenoidal sinuses are present as minute cavities at the time of birth (Onodi), but do not attain their full size until after puberty.
Intrinsic Ligaments of the Sphenoid.—The more important of these are: the pterygospinous, stretching between the spina angularis and the lateral pterygoid plate (see cervical fascia); the interclinoid, a fibrous process joining the anterior to the posterior clinoid process; and the caroticoclinoid, connecting the anterior to the middle clinoid process. These ligaments occasionally ossify.
Ethmoid bone (Os Ethmoidale) is situated at the anterior part of the base of the cranium, between the two orbits, at the roof of the nose. It consists of cribriform plate, a perpendicular plate, constituting part of the nasal septum; and two lateral labyrinths. Cribiform Plate (lamina cribrosa) is perforated by foramina carries the crista galli which borders the foramen coecum.
Ethmoid bone from above
The Labyrinth (labyrinthus ethmoidalis) consists of a number of thin-walled cellular cavities, the ethmoidal cells, arranged in three groups, anterior, middle, and posterior, and interposed between two vertical plates of bone; the lateral plate forms part of the orbit - lamina frontalis. Medially labyrinth has concha nasalis superior and concha nasalis media. There is superior nasal meatus between them.
Os Ethmoidale is exceedingly light and spongy, and cubical in shape; it is situated at the anterior part of the base of the cranium, between the two orbits, at the roof of the nose, and contributes to each of these cavities. It consists of four parts: a horizontal or cribriform plate, forming part of the base of the cranium; a perpendicular plate, constituting part of the nasal septum; and two lateral masses or labyrinths.
Cribiform Plate (lamina cribrosa; horizontal lamina).—The cribriform plate is received into the ethmoidal notch of the frontal bone and roofs in the nasal cavities. Projecting upward from the middle line of this plate is a thick, smooth, triangular process, the crista galli, so called from its resemblance to a cock’s comb. The long thin posterior border of the crista galli serves for the attachment of the falx cerebri. Its anterior border, short and thick, articulates with the frontal bone, and presents two small projecting al, which are received into corresponding depressions in the frontal bone and complete the foramen cecum. Its sides are smooth, and sometimes bulging from the presence of a small air sinus in the interior. On either side of the crista galli, the cribriform plate is narrow and deeply grooved; it supports the olfactory bulb and is perforated by foramina for the passage of the olfactory nerves. The foramina in the middle of the groove are small and transmit the nerves to the roof of the nasal cavity; those at the medial and lateral parts of the groove are larger—the former transmit the nerves to the upper part of the nasal septum, the latter those to the superior nasal concha. At the front part of the cribriform plate, on either side of the crista galli, is a small fissure which is occupied by a process of dura mater. Lateral to this fissure is a notch or foramen which transmits the nasociliary nerve; from this notch a groove extends backward to the anterior ethmoidal foramen.
Perpendicular plate of ethmoid. Shown by removing the right labyrinth.
Perpendicular Plate (lamina perpendicularis; vertical plate).—The perpendicular plate is a thin, flattened lamina, polygonal in form, which descends from the under surface of the cribriform plate, and assists in forming the septum of the nose; it is generally deflected a little to one or other side. The anterior border articulates with the spine of the frontal bone and the crest of the nasal bones. The posterior border articulates by its upper half with the sphenoidal crest, by its lower with the vomer. The inferior border is thicker than the posterior, and serves for the attachment of the septal cartilage of the nose. The surfaces of the plate are smooth, except above, where numerous grooves and canals are seen; these lead from the medial foramina on the cribriform plate and lodge filaments of the olfactory nerves.
The Labyrinth or Lateral Mass (labyrinthus ethmoidalis) consists of a number of thin-walled cellular cavities, the ethmoidal cells, arranged in three groups, anterior, middle, and posterior, and interposed between two vertical plates of bone; the lateral plate forms part of the orbit, the medial, part of the corresponding nasal cavity. In the disarticulated bone many of these cells are opened into, but when the bones are articulated, they are closed in at every part, except where they open into the nasal cavity.
Surfaces.—The upper surface of the labyrinth presents a number of half-broken cells, the walls of which are completed, in the articulated skull, by the edges of the ethmoidal notch of the frontal bone. Crossing this surface are two grooves, converted into canals by articulation with the frontal; they are the anterior and posterior ethmoidal canals, and open on the inner wall of the orbit. The posterior surface presents large irregular cellular cavities, which are closed in by articulation with the sphenoidal concha and orbital process of the palatine. The lateral surface is formed of a thin, smooth, oblong plate, the lamina papyracea (os planum), which covers in the middle and posterior ethmoidal cells and forms a large part of the medial wall of the orbit; it articulates above with the orbital plate of the frontal bone, below with the maxilla and orbital process of the palatine, in front with the lacrimal, and behind with the sphenoid.
Ethmoid bone from behind.
Ethmoid bone from the right side.
Lateral wall of nasal cavity, showing ethmoid bone in position.
In front of the lamina papyracea are some broken air cells which are overlapped and completed by the lacrimal bone and the frontal process of the maxilla. A curved lamina, the uncinate process, projects downward and backward from this part of the labyrinth; it forms a small part of the medial wall of the maxillary sinus, and articulates with the ethmoidal process of the inferior nasal concha.
The medial surface of the labyrinth forms part of the lateral wall of the corresponding nasal cavity. It consists of a thin lamella, which descends from the under surface of the cribriform plate, and ends below in a free, convoluted margin, the middle nasal concha. It is rough, and marked above by numerous grooves, directed nearly vertically downward from the cribriform plate; they lodge branches of the olfactory nerves, which are distributed to the mucous membrane covering the superior nasal concha. The back part of the surface is subdivided by a narrow oblique fissure, the superior meatus of the nose, bounded above by a thin, curved plate, the superior nasal concha; the posterior ethmoidal cells open into this meatus. Below, and in front of the superior meatus, is the convex surface of the middle nasal concha; it extends along the whole length of the medial surface of the labyrinth, and its lower margin is free and thick. The lateral surface of the middle concha is concave, and assists in forming the middle meatus of the nose. The middle ethmoidal cells open into the central part of this meatus, and a sinuous passage, termed the infundibulum, extends upward and forward through the labyrinth and communicates with the anterior ethmoidal cells, and in about 50 per cent. of skulls is continued upward as the frontonasal duct into the frontal sinus.
Ossification.—The ethmoid is ossified in the cartilage of the nasal capsule by three centers: one for the perpendicular plate, and one for each labyrinth.
The labyrinths are first developed, ossific granules making their appearance in the region of the lamina papyracea between the fourth and fifth months of fetal life, and extending into the conch. At birth, the bone consists of the two labyrinths, which are small and ill-developed. During the first year after birth, the perpendicular plate and crista galli begin to ossify from a single center, and are joined to the labyrinths about the beginning of the second year. The cribriform plate is ossified partly from the perpendicular plate and partly from the labyrinths. The development of the ethmoidal cells begins during fetal life.
Articulations.—The ethmoid articulates with fifteen bones: four of the cranium—the frontal, the sphenoid, and the two sphenoidal conch; and eleven of the face—the two nasals, two maxill, two lacrimals, two palatines, two inferior nasal conch, and the vomer.
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