I

1. General structure of vertebra. Cervical, thoracic and lumbar vertebrae

2. Sacral bone, coccyx. Ribs, sternum

3. Connection of trunk bones. Vertebral column as the whole. Thorax as the whole

 

Lesson  # 2

Theme 1.  1. Vertebrae (general data). Cervical, thoracic and lumbar vertebrae

 

Bones form the skeleton that they divide into bones of the trunk, skull, and limbs. Bones of the trunk include vertebrae, sternum and ribs.

Vertebrae

The vertebral column consists of 33-34 vertebrae: 7 cervical, 12 thoracic, 5 lumbar, 5 sacral and 4-5 coccygeal vertebrae. The sacral vertebrae fuse to form the sacrum and the coccygeal vertebrae fuse to form the coccyx. Thus the sacral and coccygeal vertebrae are false vertebrae while the others are true vertebrae.

Function of the vertebrae: 1) Supporting and amortisation; 2) Defense; 3) Motor; 4) Metabolic; 5) Hoemeopoetic.

Each vertebrae has a vertebral body and vertebral arch. They border vertebral foramen that forms the vertebral canal when vertebrae lay each other in backbone.

 

A typical thoracic vertebra, viewed from above.

 

 

Vertebral arch carries 7 processes: unpaired spinous process (projecting dorsally), paired transverse processes (for articulation with the ribs and attachment of muscles), the superior articular process and the inferior articular process processes (for articulation vertebrae each other). The vertebral notches, one caudal and one cranial, together form the intervertebral foramen which serves the passage of the spinal nerves.

Peculiarities of the III-VII Cervical Vertebrae

1.     Transverse process possesses foramen transversarium.

2.     Spinous process is bifurcated.

3.     The transverse process has an anterior tubercle and a posterior tubercle, between them we find a groove, the sulcus for the spinal nerve.

4.     Articular surfaces lay in horizontal plane.

1st Cervical Vertebra, the Atlas differs basically from the other vertebrae:

It has not any vertebral body. In the atlas we therefore describe a smaller anterior arch and a larger posterior arch. Both arches have small protuberances: the anterior and posterior tubercles. Lateral to the large vertebral foramen of the atlas lie the lateral masses, each of which has a superior and an inferior articular facet. On the inner side of the anterior arch is the articular facet for the dens, fovea dentis. From the foramen of the transverse process, which is located in the processus transversus, a groove, the sulcus arteriae vertebralis, extends across the posterior arch for the reception of the  vertebral artery.

2nd Cervical Vertebra. The Axis carries the dens or odontoid process.

On the cranial surface of the body the axis carries a tooth-like process, the dens axis, which ends in a rounded point, the apex dentis. The surfaces of the dens have a the anterior articular facet and the posterior articular facet.

The anterior tubercle of the 6th cervical vertebra can be very large and is designated as the carotid tubercle.

The 7th cervical vertebra has a particularly large spinous process, which is usually the highest palpable spinous process of the vertebral column; it is therefore called the vertebra prominens.

Peculiarities of the Thoracic Vertebrae

1.  Laterally, the vertebral body usually has two costal facets, each of which is half of an articular facet for articulation with the head of a rib.

2.  Transverse processes carry a costal facet for articulation with the costal tubercle.

3.  The spinous processes of the 1-st through the 9th thoracic vertebrae overlap each other like roof tiles.

4.  Articular surfaces lay in frontal plane.

5. 

The 1^st thoracic vertebra has a complete articular facet at the cranial border of its body and a half facet at the caudal border. The 10^th vertebra has only a half articular facet, while the 11th has a complete articular facet at its cranial border. The 12th thoracic vertebra has the articular facet for the head of the rib in the middle of the lateral surface of the body. There may be an accessory process and a mamillary processor each side.

 

 

 

Peculiarities of the Lumbar Vertebrae

1.  The bodies of the are much larger than those of the other vertebrae.

2.  The spinous process is flat and is directed sagittally.

3.  The flattened lateral processes of the lumbar vertebrae may be called costal processes, and since they originate from rib aniagen.

4.  Articular surfaces lay in sagittal plane.

5.  Arch carries the mamillar and accessory processes.

 

 

 

 

 

 

 

The anatomical position. For descriptive purposes the body is always imagined to be in the anatomical position, standing erect, arms by sides, palms of hands facing forwards. In this position directions are given by superior, inferior, anterior, posterior. These are equivalent to the zoologists cephalad, caudad, ventral and dorsal. Thus the eyes are always superior to the mouth, even if the patient is lying down or standing on his head. These terms are not quite equivalent to above, below, in front of and behind. To a layman an acrobats feet are above her head when she is dangling from a trapeze: to an anatomist they are inferior.

 

 

 

 

Other dimensions are referred to the midline - median, medial or lateral, or to their closeness to the body surface, superficial or deep. In the limbs structures near the trunk are proximal, those further away are distal. We have a problem with the hands and feet: the palms of the hands resemble the soles of the feet and the thumb is equivalent to the great toe. But the palmar surface of the hand faces anteriorly and the back is dorsal. In the foot we defy logic and call the inferior surface plantar (equivalent to palmar) and the superior surface dorsal, even though it faces upwards. But we are still not out of the wood because the great toe is medial but the thumb is lateral. To get around this the term preaxial is often used to describe the thumb or great toe side. Postaxial is the little toe or little finger side. The axis referred to runs to the tip of the middle finger or the second toe. The other small problem, the penis, is described in it's erect position, so that its dorsal surface faces anteriorly and superiorly when detumescent.

We also need to define planes, mutually at right angles. The horizontal plane is clear enough: the other two are a little less so. The sagittal plane probably refers to the sagittal suture which runs from anterior to posterior in the newborn skull, and has an arrowhead in the form of the frontal fontanelle. Coronal is also difficult since it means crown, and I always think of a crown as being horizontal. But this is an older usage, as in the crown of an arch or a tooth, or the road, meaning something more like a halo.

Hand and foot again pose problems because of their distinctive orientation. The hand has a rather unusual movement whereby the thumb can be brought to lie medially: in fact this crosses the bones of the forearm. The anatomical position of the hand is called supine, the reverse prone, so this movement is pronation reverse supination.

Abduction and adduction of the digits are refereed to the axis of the hand or foot, which remember pass through the middle finger and the second toe. We also have a thumb problem. Finger nails are posterior, but that of the thumb lies at right angles to the others. The thumb normally lies with its palmar surface facing medially. Flexion and extension are thus in a coronal plane while abduction and adduction are sagittal. The thumb also has another important movement, opposition which brings its palmar surface in contact with the palmar surface of the fingers.

The feet also bring problems, so we talk of dorsiflexion and plantar flexion and, a unique foot movement inversion and eversion as the soles are made to point towards each other or away.

One important fact which an anatomist must recognise is that no two of us, even identical twins are exactly alike. The structure of the body varies with age, race, sex, genetic, diversity, environmental history (especially during growth)

 Although this is a whole field in itself it is important to recognise the commonest changes due to age, since you will be looking mainly at aged cadavers and young, fit adults. Bear in mind that an 80 year old will differ in these respects: connective tissue - less elasticity - wrinkles cartilage - less elasticity - degenerative changes such as osteo-arthritis with associated changes. Costal cartilages often replaced by bone: bony spurs develop in unusual places. Bone - becomes brittle, reduced in size with less activity. Muscle - ditto, plus deposition of fat. Heart and blood vessels - arteries become tortuous, walls become furred up with atheroma. Left ventricle is enlarged as consequence of load. Veins often varicose. Nervous system - Often small strokes will cause paralysis and reduction in size of some muscles.

          This is a tricky one because of its emotive content, and because of the difficulty in defining race since the invention of the bicycle, steamship, jumbo jet etc. have done much to cause intermingling. Carefully noting the distinction between racism and Racialism we can say that there are obvious differences in skin and hair colour, hair type, eye colour, etc. and some subtle but small differences in anatomical measurements.

 The two sexes obviously differ in their reproductive organs: they also differ in many other respects: although variability is quite large within a sex height, weight and muscle mass will differ significantly. Males also have narrower hips and broader shoulders. Females have more dermal fat, distributed differently. Facial and body hair also differs.

 There is quite a high level of genetic and environmental variation which leads to the presence of extra fingers, a single kidney, or an extra rib or so. This may be genetical or due to the exposure of the fetus to something unpleasant during pregnancy - x-rays, medicaments, viruses. Superimposed upon this is the variation due to habit - a regular swimmer will have a better developed upper body than his or her classmates: a smoker may have inferior lung capacity.

 

The allantois arises as a tubular diverticulum of the posterior part of the yolk-sac; when the hind-gut is developed the allantois is carried backward with it and then opens into the cloaca or terminal part of the hind-gut: it grows out into the body-stalk, a mass of mesoderm which lies below and around the tail end of the embryo. The diverticulum is lined by entoderm and covered by mesoderm, and in the latter are carried the allantoic or umbilical vessels.

In reptiles, birds, and many mammals the allantois becomes expanded into a vesicle which projects into the extra-embryonic celom. If its further development be traced in the bird, it is seen to project to the right side of the embryo, and, gradually expanding, it spreads over its dorsal surface as a flattened sac between the amnion and the serosa, and extending in all directions, ultimately surrounds the yolk. Its outer wall becomes applied to and fuses with the serosa, which lies immediately inside the shell membrane. Blood is carried to the allantoic sac by the two allantoic or umbilical arteries, which are continuous with the primitive aortæ, and after circulating through the allantoic capillaries, is returned to the primitive heart by the two umbilical veins. In this way the allantoic circulation, which is of the utmost importance in connection with the respiration and nutrition of the chick, is establishedIn man and other primates the nature of the allantois is entirely different from that just described. Here it exists merely as a narrow, tubular diverticulum of the hind-gut, and never assumes the form of a vesicle outside the embryo. With the formation of the amnion the embryo is, in most animals, entirely separated from the chorion, and is only again united to it when the allantoic mesoderm spreads over and becomes applied to its inner surface.

The amnion is a membranous sac which surrounds and protects the embryo. It is developed in reptiles, birds, and mammals, which are hence called “Amniota;” but not in amphibia and fishes, which are consequently termed “Anamnia.”

In the human embryo the earliest stages of the formation of the amnion have not been observed; in the youngest embryo which has been studied the amnion was already present as a closed sac and, as indicated on page 46, appears in the inner cell-mass as a cavity. This cavity is roofed in by a single stratum of flattened, ectodermal cells, the amniotic ectoderm, and its floor consists of the prismatic ectoderm of the embryonic disk—the continuity between the roof and floor being established at the margin of the embryonic disk. Outside the amniotic ectoderm is a thin layer of mesoderm, which is continuous with that of the somatopleure and is connected by the body-stalk with the mesodermal lining of the chorion.

When first formed the amnion is in contact with the body of the embryo, but about the fourth or fifth week fluid (liquor amnii) begins to accumulate within it. This fluid increases in quantity and causes the amnion to expand and ultimately to adhere to the inner surface of the chorion, so that the extra-embryonic part of the celom is obliterated. The liquor amnii increases in quantity up to the sixth or seventh month of pregnancy, after which it diminishes somewhat; at the end of pregnancy it amounts to about 1 liter. It allows of the free movements of the fetus during the later stages of pregnancy, and also protects it by diminishing the risk of injury from without. It contains less than 2 per cent. of solids, consisting of urea and other extractives, inorganic salts, a small amount of protein, and frequently a trace of sugar. That some of the liquor amnii is swallowed by the fetus is proved by the fact that epidermal debris and hairs have been found among the contents of the fetal alimentary canal.

In reptiles, birds, and many mammals the amnion is developed in the following manner: At the point of constriction where the primitive digestive tube of the embryo joins the yolk-sac a reflection or folding upward of the somatopleure takes place. This, the amniotic fold first makes its appearance at the cephalic extremity, and subsequently at the caudal end and sides of the embryo, and gradually rising more and more, its different parts meet and fuse over the dorsal aspect of the embryo, and enclose a cavity, the amniotic cavity. After the fusion of the edges of the amniotic fold, the two layers of the fold become completely separated, the inner forming the amnion, the outer the false amnion or serosa. The space between the amnion and the serosa constitutes the extra-embryonic celom, and for a time communicates with the embryonic celom.

         Diagram of a transverse section, showing the mode of formation of the amnion in the chick. The amniotic folds have nearly united in the middle line.

Bones form the skeleton that they divide into bones of the trunk, skull, and limbs. Bones of the trunk comprise vertebrae, sternum and ribs.

Vertebrae.

The vertebral column consists of 33-34 vertebrae: 7 cervical, 12 thoracic, 5 lumbar, 5 sacral and 4-5 coccygeal vertebrae. The sacral vertebrae fuse and form the sacrum and the coccygeal vertebrae fuse togather and form the coccyx. Thus the sacral and coccygeal vertebrae are false vertebrae while the others are true vertebrae.

Function of the vertebrae: 1) Supporting and amortisation; 2) Defence; 3) Motor; 4) Metabolic; 5) Hoemeopoetic.

Each vertebrae has a vertebral corpus (body) and vertebral arch. They border vertebral foramina that form the vertebral canal when vertebrae lay each other in backbone. Vertebral arch carries 7 processes: unpaired spinous process (projecting dorsally), paired transverse processes (for articulation with the ribs), the superior articular process and the inferior articular process processes (for articulation vertebrae each other). The vertebral notches, one caudal and one cranial, together form the intervertebral foramen, which serves the passage of the spinal nerves.

Peculiarities of the III-VII cervical vertebrae

                        1. Transverse process carry foramen transversarium.

                        2. Spinous process is bifurcated.

                        3. The transverse process has an anterior tubercle and a posterior tubercle, between them we find a groove, the sulcus for the spinal nerve.

          4. Articular surfaces lay in horizontal plane.

1st cervical vertebra, the atlas differs basically from the other vertebrae:

It has not any vertebral body. In the atlas we therefore describe a smaller anterior arch and a larger posterior arch. Both arches have small protuberances: the anterior and posterior tubercles. Lateral to the large vertebral foramen of the atlas lie the

lateral masses, each of which have a superior and an inferior articular facet. On the inner side of the anterior arch is the articular facet for the dens, fovea dentis. From the foramen of the transverse process, which is located in the processus transversus, a groove, the sulcus arteriae vertebralis, extends across the posterior arch for the reception of the vertebral artery. 2nd cervical vertebra. The axis carries the dens or odontoid process. On the cranial surface of the body the axis carries a tooth-like process, the dens, which ends by the apex dentis. The surfaces of the dens have an anterior articular facet and the posterior articular facet. The anterior tubercle of the 6th cervical vertebra can be very large and is designated as the carotid tubercle. The 7th cervical vertebra has a particularly large spinous process, which is usually the highest palpable spinous process of the vertebral column; it is therefore called the vertebra prominens. Peculiarities of the thoracic vertebrae

                       1. Laterally, the vertebral body usually has two costal facets, each of which is half of an articular facet for articulation with the head of a rib.

                       2. Transverse processes carry a costal facet for articulation with the costal tubercle.

                       3. The spinous processes of the 1^st through the 9th thoracic vertebrae overlap each other like roof tiles.

                       4. Articular surfaces lay in frontal plane.

The 1st thoracic vertebra has a complete articular facet at the cranial border of its body and a half facet at the caudal border. The 10th vertebra has only a half articular facet, while the 11th has a complete articular facet at its cranial border. The 12th thoracic vertebra has the articular facet for the head of the rib in the middle of the lateral surface of the body. There may be an accessory process and a mamillary process each side.

 

 

 

Theme 2. Sacral bone, coccyx. Ribs, sternum

 

 

 

 

Peculiarities of the Sacral Vertebrae

 

The sacrum consists of the five fused sacral vertebrae. It has a concave anterior or pelvic surface and a convex dorsal surface. The sacrum has the base (with promontory) and the apex.

 

 

 

 

 

 

 

 

 

The pelvic surface has four paired pelvic anterior sacral foramina and transverse lines. In the convex dorsal surface there are posterior sacral foramina and five longitudinal ridges, not always clearly developed, have their origin in fusion of the corresponding processes of the vertebrae (median sacral, intermediate sacral and lateral sacral crests).

 The sacral canal is located in bone and it terminate by the sacral hiatus, bounded laterally by the two sacral horns. Auricular surface for the articulation with the hip bone and sacral tuberosity can be seen in lateral parts.

 

Coccyx

 

 

 

 

 

 

The coccyx, which is usually formed from three to four vertebrae, has body and cornua or horns.

 

Theme 3. Connection of trunk bones. Vertebral column as the whole. Thorax as the whole

 

 

 

 

 

The vertebral column is situated in the median line, as the posterior part of the trunk; its average length in the male is about 71 cm.

 

 

Of this length the cervical part measures 12.5 cm., the thoracic about 28 cm., the lumbar 18 cm., and the sacrum and coccyx 12.5 cm. The female column is about 61 cm. in length.

 

 

 

                                                                 

Curves.—Viewed laterally the vertebral column presents several curves, which correspond to the different regions of the column, and are called cervical, thoracic, lumbar, and pelvic. The cervical curve, convex forward, begins at the apex of the odontoid process, and ends at the middle of the second thoracic vertebra; it is the least marked of all the curves. The thoracic curve, concave forward, begins at the middle of the second and ends at the middle of the twelfth thoracic vertebra. Its most prominent point behind corresponds to the spinous process of the seventh thoracic vertebra. The lumbar curve is more marked in the female than in the male; it begins at the middle of the last thoracic vertebra, and ends at the sacrovertebral angle. It is convex anteriorly, the convexity of the lower three vertebræ being much greater than that of the upper two.

 

 

 

The pelvic curve begins at the sacrovertebral articulation, and ends at the point of the coccyx; its concavity is directed downward and forward. The thoracic and pelvic curves are termed primary curves, because they alone are present during fetal life. The cervical and lumbar curves are compensatory or secondary, and are developed after birth, the former when the child is able to hold up its head (at three or four months), and to sit upright (at nine months), the latter at twelve or eighteen months, when the child begins to walk.

 

                                      

  The vertebral column has also a slight lateral curvature, the convexity of which is directed toward the right side. This may be produced by muscular action, most persons using the right arm in preference to the left, especially in making long-continued efforts, when the body is curved to the right side. In support of this explanation it has been found that in one or two individuals who were left-handed, the convexity was to the left side.

 

 

 By others this curvature is regarded as being produced by the aortic arch and upper part of the descending thoracic aorta—a view which is supported by the fact that in cases where the viscera are transposed and the aorta is on the right side, the convexity of the curve is directed to the left side.                 

Surfaces.—Anterior Surface.—When viewed from in front, the width of the bodies of the vertebræ is seen to increase from the second cervical to the first thoracic; there is then a slight diminution in the next three vertebræ; below this there is again a gradual and progressive increase in width as low as the sacrovertebral angle. From this point there is a rapid diminution, to the apex of the coccyx.                                                             

Posterior Surface.—The posterior surface of the vertebral column presents in the median line the spinous processes. In the cervical region (with the exception of the second and seventh vertebræ) these are short and horizontal, with bifid extremities. In the upper part of the thoracic region they are directed obliquely downward; in the middle they are almost vertical, and in the lower part they are nearly horizontal. In the lumbar region they are nearly horizontal. The spinous processes are separated by considerable intervals in the lumbar region, by narrower intervals in the neck, and are closely approximated in the middle of the thoracic region. Occasionally one of these processes deviates a little from the median line—a fact to be remembered in practice, as irregularities of this sort are attendant also on fractures or displacements of the vertebral column.

 

 

On either side of the spinous processes is the vertebral groove formed by the laminæ in the cervical and lumbar regions, where it is shallow, and by the laminæ and transverse processes in the thoracic region, where it is deep and broad; these grooves lodge the deep muscles of the back.

 

 

 Lateral to the vertebral grooves are the articular processes, and still more laterally the transverse processes. In the thoracic region, the transverse processes stand backward, on a plane considerably behind that of the same processes in the cervical and lumbar regions. In the cervical region, the transverse processes are placed in front of the articular processes, lateral to the pedicles and between the intervertebral foramina. In the thoracic region they are posterior to the pedicles, intervertebral foramina, and articular processes. In the lumbar region they are in front of the articular processes, but behind the intervertebral foramina.

 

 

           Lateral Surfaces.—The lateral surfaces are separated from the posterior surface by the articular processes in the cervical and lumbar regions, and by the transverse processes in the thoracic region. They present, in front, the sides of the bodies of the vertebræ, marked in the thoracic region by the facets for articulation with the heads of the ribs. More posteriorly are the intervertebral foramina, formed by the juxtaposition of the vertebral notches, oval in shape, smallest in the cervical and upper part of the thoracic regions, and gradually increasing in size to the last lumbar. They transmit the spinal nerves and are situated between the transverse processes in the cervical region, and in front of them in the thoracic and lumbar regions.

                                                                                                                       

Video 4

 

 

 

Vertebral Canal.—The vertebral canal follows the different curves of the column; it is large and triangular in those parts of the column which enjoy the greatest freedom of movement, viz., the cervical and lumbar regions; and is small and rounded in the thoracic region, where motion is more limited. All vertebrae compose vertebral column, which has cervical and lumbal curves forward (lordosis), and thoracic and sacral curves backward (kyphosis).

Articulations of the Vertebral Column consist of (1) a series of amphiarthrodial joints between the vertebral bodies, and (2) a series of diathrodial joints between the vertebral arches.            

  1. Articulations of Vertebral Bodies (intercentral ligaments).—The articulations between the bodies of the vertebræ are amphiarthrodial joints, and the individual vertebræ move only slightly on each other. When, however, this slight degree of movement between the pairs of bones takes place in all the joints of the vertebral column, the total range of movement is very considerable. The ligaments of these articulations are the following:             

The Anterior Longitudinal.             The Posterior Longitudinal.

The Intervertebral Fibrocartilages.

                                                                                                                   

                                                                                                                   

The Anterior Longitudinal Ligament (ligamentum longitudinale anterius; anterior common ligament) is a broad and strong band of fibers, which extends along the anterior surfaces of the bodies of the vertebræ, from the axis to the sacrum. It is broader below than above, thicker in the thoracic than in the cervical and lumbar regions, and somewhat thicker opposite the bodies of the vertebræ than opposite the intervertebral fibrocartilages. It is attached, above, to the body of the axis, where it is continuous with the anterior atlantoaxial ligament, and extends down as far as the upper part of the front of the sacrum. It consists of dense longitudinal fibers, which are intimately adherent to the intervertebral fibrocartilages and the prominent margins of the vertebræ, but not to the middle parts of the bodies. In the latter situation the ligament is thick and serves to fill up the concavities on the anterior surfaces, and to make the front of the vertebral column more even. It is composed of several layers of fibers, which vary in length, but are closely interlaced with each other. The most superficial fibers are the longest and extend between four or five vertebræ. A second, subjacent set extends between two or three vertebræ while a third set, the shortest and deepest, reaches from one vertebra to the next. At the sides of the bodies the ligament consists of a few short fibers which pass from one vertebra to the next, separated from the concavities of the vertebral bodies by oval apertures for the passage of vessels.                                                                              4

 

 

Median sagittal section of two lumbar vertebræ and their ligaments

                                                                                                                   

                                                                                                                   

The Posterior Longitudinal Ligament (ligamentum longitudinale posterius; posterior common ligament) is situated within the vertebral canal, and extends along the posterior surfaces of the bodies of the vertebræ, from the body of the axis, where it is continuous with the membrana tectoria, to the sacrum. It is broader above than below, and thicker in the thoracic than in the cervical and lumbar regions. In the situation of the intervertebral fibrocartilages and contiguous margins of the vertebræ, where the ligament is more intimately adherent, it is broad, and in the thoracic and lumbar regions presents a series of dentations with intervening concave margins; but it is narrow and thick over the centers of the bodies, from which it is separated by the basivertebral veins. This ligament is composed of smooth, shining, longitudinal fibers, denser and more compact than those of the anterior ligament, and consists of superficial layers occupying the interval between three or four vertebræ, and deeper layers which extend between adjacent vertebræ.                                            

                                                                                                                   

The Intervertebral Fibrocartilages (fibrocartilagines intervertebrales; intervertebral disks) are interposed between the adjacent surfaces of the bodies of the vertebræ, from the axis to the sacrum, and form the chief bonds of connection between the vertebræ. They vary in shape, size, and thickness, in different parts of the vertebral column. In shape and size they correspond with the surfaces of the bodies between which they are placed, except in the cervical region, where they are slightly smaller from side to side than the corresponding bodies. In thickness they vary not only in the different regions of the column, but in different parts of the same fibrocartilage; they are thicker in front than behind in the cervical and lumbar regions, and thus contribute to the anterior convexities of these parts of the column; while they are of nearly uniform thickness in the thoracic region, the anterior concavity of this part of the column being almost entirely owing to the shape of the vertebral bodies. The intervertebral fibrocartilages constitute about one-fourth of the length of the vertebral column, exclusive of the first two vertebræ; but this amount is not equally distributed between the various bones, the cervical and lumbar portions having, in proportion to their length, a much greater amount than the thoracic region, with the result that these parts possess greater pliancy and freedom of movement. The intervertebral fibrocartilages are adherent, by their surfaces, to thin layers of hyaline cartilage which cover the upper and under surfaces of the bodies of the vertebræ; in the lower cervical vertebræ, however, small joints lined by synovial membrane are occasionally present between the upper surfaces of the bodies and the margins of the fibrocartilages on either side. By their circumferences the intervertebral fibrocartilages are closely connected in front to the anterior, and behind to the posterior, longitudinal ligaments. In the thoracic region they are joined laterally, by means of the interarticular ligaments, to the heads of those ribs which articulate with two vertebræ.                                                               

 

 

Posterior longitudinal ligament, in the thoracic region

                                                                                                                   

                                                                                                                   

Structure of the Intervertebral Fibrocartilages.—Each is composed, at its circumference, of laminæ of fibrous tissue and fibrocartilage, forming the annulus fibrosus; and, at its center, of a soft, pulpy, highly elastic substance, of a yellowish color, which projects considerably above the surrounding level when the disk is divided horizontally. This pulpy substance (nucleus pulposus), especially well-developed in the lumbar region, is the remains of the notochord. The laminæ are arranged concentrically; the outermost consist of ordinary fibrous tissue, the others of white fibrocartilage. The laminæ are not quite vertical in their direction, those near the circumference being curved outward and closely approximated; while those nearest the center curve in the opposite direction, and are somewhat more widely separated. The fibers of which each lamina is composed are directed, for the most part, obliquely from above downward, the fibers of adjacent laminæ passing in opposite directions and varying in every layer; so that the fibers of one layer are directed across those of another, like the limbs of the letter X. This laminar arrangement belongs to about the outer half of each fibrocartilage. The pulpy substance presents no such arrangement, and consists of a fine fibrous matrix, containing angular cells united to form a reticular structure.                                           

  The intervertebral fibrocartilages are important shock absorbers. Under pressure the highly elastic nucleus pulposus becomes flatter and broader and pushes the more resistant fibrous laminæ outward in all directions.                                                                   

  2. Articulations of Vertebral Arches.—The joints between the articular processes of the vertebræ belong to the arthrodial variety and are enveloped by capsules lined by synovial membranes; while the laminæ, spinous and transverse processes are connected by the following ligaments:                                                                                       

The Ligamenta Flava.   The Ligamentum Nuchæ.

The Supraspinal.         The Interspinal.

The Intertransverse.

                                                                                                                   

                                                                                                                   

The Articular Capsules (capsulæ articulares; capsular ligaments) are thin and loose, and are attached to the margins of the articular processes of adjacent vertebræ. They are longer and looser in the cervical than in the thoracic and lumbar regions.                       

                                                                                                                   

The Ligamenta Flava ligamenta subflava connect the laminæ of adjacent vertebræ, from the axis to the first segment of the sacrum. They are best seen from the interior of the vertebral canal; when looked at from the outer surface they appear short, being overlapped by the laminæ. Each ligament consists of two lateral portions which commence one on either side of the roots of the articular processes, and extend backward to the point where the laminæ meet to form the spinous process; the posterior margins of the two portions are in contact and to a certain extent united, slight intervals being left for the passage of small vessels. Each consists of yellow elastic tissue, the fibers of which, almost perpendicular in direction, are attached to the anterior surface of the lamina above, some distance from its inferior margin, and to the posterior surface and upper margin of the lamina below. In the cervical region the ligaments are thin, but broad and long; they are thicker in the thoracic region, and thickest in the lumbar region. Their marked elasticity serves to preserve the upright posture, and to assist the vertebral column in resuming it after flexion.                                                 

 

 

Vertebral arches of three thoracic vertebræ viewed from the front

                                                                                                                   

 The Supraspinal Ligament (ligamentum supraspinale; supraspinous ligament) is a strong fibrous cord, which connects together the apices of the spinous processes from the seventh cervical vertebra to the sacrum; at the points of attachment to the tips of the spinous processes fibrocartilage is developed in the ligament. It is thicker and broader in the lumbar than in the thoracic region, and intimately blended, in both situations, with the neighboring fascia. The most superficial fibers of this ligament extend over three or four vertebræ; those more deeply seated pass between two or three vertebræ while the deepest connect the spinous processes of neighboring vertebræ. Between the spinous processes it is continuous with the interspinal ligaments. It is continued upward to the external occipital protuberance and median nuchal line, as the ligamentum nuchæ.                                                                       

                                                                                                                   

The Ligamentum Nuchæ.—The ligamentum nuchæ is a fibrous membrane, which, in the neck, represents the supraspinal ligaments of the lower vertebræ. It extends from the external occipital protuberance and median nuchal line to the spinous process of the seventh cervical vertebra. From its anterior border a fibrous lamina is given off, which is attached to the posterior tubercle of the atlas, and to the spinous processes of the cervical vertebræ, and forms a septum between the muscles on either side of the neck. In man it is merely the rudiment of an important elastic ligament, which, in some of the lower animals, serves to sustain the weight of the head.                                                                                                         

                                                                                                                   

The Interspinal Ligaments (ligamenta interspinalia; interspinous ligaments) The interspinal ligaments thin and membranous, connect adjoining spinous processes and extend from the root to the apex of each process. They meet the ligamenta flava in front and the supraspinal ligament behind. They are narrow and elongated in the thoracic region; broader, thicker, and quadrilateral in form in the lumbar region; and only slightly developed in the neck.     

                                                                                                                   

The Intertransverse Ligaments (ligamenta intertransversaria).—The intertransverse ligaments are interposed between the transverse processes. In the cervical region they consist of a few irregular, scattered fibers; in the thoracic region they are rounded cords intimately connected with the deep muscles of the back; in the lumbar region they are thin and membranous.   

                                                                                                                   

Movements.—The movements permitted in the vertebral column are: flexion, extension, lateral movement, circumduction, and rotation.                                                         

  In flexion, or movement forward, the anterior longitudinal ligament is relaxed, and the intervertebral fibrocartilages are compressed in front; while the posterior longitudinal ligament, the ligamenta flava, and the inter- and supraspinal ligaments are stretched, as well as the posterior fibers of the intervertebral fibrocartilages. The interspaces between the laminæ are widened, and the inferior articular processes glide upward, upon the superior articular processes of the subjacent vertebræ. Flexion is the most extensive of all the movements of the vertebral column, and is freest in the lumbar region.                                      

  In extension, or movement backward, an exactly opposite disposition of the parts takes place. This movement is limited by the anterior longitudinal ligament, and by the approximation of the spinous processes. It is freest in the cervical region.    

  In lateral movement, the sides of the intervertebral fibrocartilages are compressed, the extent of motion being limited by the resistance offered by the surrounding ligaments. This movement may take place in any part of the column, but is freest in the cervical and lumbar regions.    

  Circumduction is very limited, and is merely a succession of the preceding movements.    

  Rotation is produced by the twisting of the intervertebral fibrocartilages; this, although only slight between any two vertebræ, allows of a considerable extent of movement when it takes place in the whole length of the column, the front of the upper part of the column being turned to one or other side. This movement occurs to a slight extent in the cervical region, is freer in the upper part of the thoracic region, and absent in the lumbar region.         

  The extent and variety of the movements are influenced by the shape and direction of the articular surfaces. In the cervical region the upward inclination of the superior articular surfaces allows of free flexion and extension. Extension can be carried farther than flexion; at the upper end of the region it is checked by the locking of the posterior edges of the superior atlantal facets in the condyloid fossæ of the occipital bone; at the lower end it is limited by a mechanism whereby the inferior articular processes of the seventh cervical vertebra slip into grooves behind and below the superior articular processes of the first thoracic. Flexion is arrested just beyond the point where the cervical convexity is straightened; the movement is checked by the apposition of the projecting lower lips of the bodies of the vertebræ with the shelving surfaces on the bodies of the subjacent vertebræ. Lateral flexion and rotation are free in the cervical region; they are, however, always combined. The upward and medial inclinations of the superior articular surfaces impart a rotary movement during lateral flexion, while pure rotation is prevented by the slight medial slope of these surfaces.      

  In the thoracic region, notably in its upper part, all the movements are limited in order to reduce interference with respiration to a minimum. The almost complete absence of an upward inclination of the superior articular surfaces prohibits any marked flexion, while extension is checked by the contact of the inferior articular margins with the laminæ, and the contact of the spinous processes with one another. The mechanism between the seventh cervical and the first thoracic vertebræ, which limits extension of the cervical region, will also serve to limit flexion of the thoracic region when the neck is extended. Rotation is free in the thoracic region: the superior articular processes are segments of a cylinder whose axis is in the mid-ventral line of the vertebral bodies. The direction of the articular facets would allow of free lateral flexion, but this movement is considerably limited in the upper part of the region by the resistance of the ribs and sternum.                                                                                           

  In the lumbar region flexion and extension are free. Flexion can be carried farther than extension, and is possible to just beyond the straightening of the lumbar curve; it is, therefore, greatest at the lowest part where the curve is sharpest. The inferior articular facets are not in close apposition with the superior facets of the subjacent vertebræ, and on this account a considerable amount of lateral flexion is permitted. For the same reason a slight amount of rotation can be carried out, but this is so soon checked by the interlocking of the articular surfaces that it is negligible.                                                                       

Thorax

 

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 5 cm., and its transverse diameter about 10 cm. The lower opening is formed by the twelfth thoracic vertebra behind, by the eleventh and twelfth ribs at the sides, and in front by the cartilages of the tenth, ninth, eighth, and seventh ribs, which ascend on either side and form an angle, the subcostal angle, into the apex of which the xiphoid process projects. The lower opening is wider transversely than from before backward, and slopes obliquely downward and backward, it is closed by the diaphragm which forms the floor of the thorax.

 

 

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.

 

 

 

Проміжна проекція

 

VIDEO

 

 

 

References:

1.Gray`s Anatomy. Lawrence H. Bannister, Martin M. Berry, Patricia Collins and others. Churchhill Livingstone, - 1999. 2092 p.

2. W. Kahle, H. Leonhardt, W. Platzer. Colour atlas and Textbook of Human Anatomy. – Stuttgart, New York, 1986.

3. R.D. Lockhart, G.F. Hamilton, F.W. Fyfe. Anatomy of the human body. – Philadelphia.

4. F.H. Netter. Atlas of Human Anatomy. – Cіba Pharmaceutіcals Dіvіsіon, 1994. – 514 p.

5. Synelnіkov R.D. The atlas of anatomy of the man. Іn the 4-th volumes. -: Medіcіna, 1991.

6. Lecture.

7. Colіn H. Wheatley, B.Kolz. Human anatomy and physіology. 1995.

8. Reminetskyy B.Y., Fedonyuk Y.I. Human anatomy. Locomotory apparatus. Notes. ‘Ukrmedknyha’,  - 2002, - 136 p.