Skull as A whole. Cranial BASE and calvaria. BONY PALATE. TEMPORAL, INFRATEMPORAL, PTERYGOPA-LATINE FOSSAE.
Orbit. Nasal cavity
Lesson # 4
Theme 1. Skull as whole. Cranial BASE and calvaria. BONY PALATE. TEMPORAL, INFRATEMPORAL, PTERYGOPALA-TINE FOSSAE
Pterygopalatine fossa formed anteriorly by maxillary body, posteriorly by base of pterygoid process of the sphenoid bone and medially - by the perpendicular plate of the palatine bone. Prygopalatine fossa communicates with internal cranial base through foramen rotundum, with orbit thruogh inferior orbital fissura, with mouth cavity through greater and lesser palatine canals, with external cranial base (foramen lacerum) through pterygoid canal.
The Pterygopalatine Fossa (fossa pterygopalatina; sphenomaxillary fossa).—The pterygopalatine fossa is a small, triangular space at the angle of junction of the inferior orbital and pterygomaxillary fissures, and placed beneath the apex of the orbit. It is bounded above by the under surface of the body of the sphenoid and by the orbital process of the palatine bone; in front, by the infratemporal surface of the maxilla; behind, by the base of the pterygoid process and lower part of the anterior surface of the great wing of the sphenoid; medially, by the vertical part of the palatine bone with its orbital and sphenoidal processes.
This fossa communicates with the orbit by the inferior orbital fissure, with the nasal cavity by the sphenopalatine foramen, and with the infratemporal fossa by the pterygomaxillary fissure. Five foramina open into it. Of these, three are on the posterior wall, viz., the foramen rotundum, the pterygoid canal, and the pharyngeal canal, in this order downward and medialward. On the medial wall is the sphenopalatine foramen, and below is the superior orifice of the pterygopalatine canal. The fossa contains the maxillary nerve, the sphenopalatine ganglion, and the terminal part of the internal maxillary artery.
The skull is the skeleton of the head, a series of bones from its two parts, the Neurocranium and Facial skull. The neurocranium provides a case for the brain and cranial meninges, proximal parts of the cranial nerves, and blood vessels.
The term cranium (means skull) is sometimes restricted to a skull without the mandible. The cranium has a domelike root – the Calvaria – skullcap – and a floor or cranial base consisting of the ethmoid bone and parts of the occipital and temporal bones. The facial skeleton consists of the bones surrounding the mouth and nose and contributing to the orbits (eye sockets, orbital cavities). In the anatomical position, the skull is oriented so that the inferior margin of the orbit (eye socket) and the superior margin of the external acustic meatus (auditory canal) are horizontal.
The skull as a whole may be viewed from different points, and the views so obtained are termed the normæ of the skull; thus, it may be examined from above (norma verticalis), from below (norma basalis), from the side (norma lateralis), from behind (norma occipitalis), or from the front (norma frontalis).
Norma Verticalis.—When viewed from above the outline presented varies greatly in different skulls; in some it is more or less oval, in others more nearly circular. The surface is traversed by three sutures, viz.: (1) the coronal sutures, nearly transverse is direction, between the frontal and parietals; (2) the sagittal sutures, medially placed, between the parietal bones, and deeply serrated in its anterior two-thirds; and (3) the upper part of the lambdoidal suture, between the parietals and the occipital. The point of junction of the sagittal and coronal suture is named the bregma, that of the sagittal and lambdoid sutures, the lambda; they indicate respectively the positions of the anterior and posterior fontanelles in the fetal skull. On either side of the sagittal suture are the parietal eminence and parietal foramen—the latter, however, is frequently absent on one or both sides. The skull is often somewhat flattened in the neighborhood of the parietal foramina, and the term obelion is applied to that point of the sagittal suture which is on a level with the foramina. In front is the glabella, and on its lateral aspects are the superciliary arches, and above these the frontal eminences. Immediately above the glabella may be seen the remains of the frontal suture; in a small percentage of skulls this suture persists and extends along the middle line to the bregma. Passing backward and upward from the zygomatic processes of the frontal bone are the temporal lines, which mark the upper limits of the temporal fossæ. The zygomatic arches may or may not be seen projecting beyond the anterior portions of these lines.
Base of skull. Inferior surface.
inferior surface of the base of the skull, exclusive of the mandible, is
bounded in front by the incisor teeth in the maxillæ;
behind, by the superior nuchal lines of the occipital; and laterally by the
alveolar arch, the lower border of the zygomatic
bone, the zygomatic arch and an imaginary line
extending from it to the mastoid process and extremity of the superior nuchal
line of the occipital. It is formed by the palatine processes of the maxillæ and palatine bones, the vomer,
the pterygoid processes, the under surfaces of the
great wings, spinous processes, and part of the body
of the sphenoid, the under surfaces of the squamæ
and mastoid and petrous portions of the temporals,
and the under surface of the occipital bone. The anterior part or hard palate
projects below the level of the rest of the surface, and is bounded in front
and laterally by the alveolar arch containing the sixteen teeth of the maxillæ. Immediately behind the incisor teeth is the incisive
foramen. In this foramen are two lateral apertures, the openings of the incisive
canals (foramina of Stenson) which
transmit the anterior branches of the descending palatine vessels, and the nasopalatine nerves. Occasionally two additional canals are
present in the incisive foramen; they are termed the foramina of Scarpa and are situated in the middle line; when
present they transmit the nasopalatine nerves. The
vault of the hard palate is concave, uneven, perforated by numerous foramina,
marked by depressions for the palatine glands, and traversed by a crucial
suture formed by the junction of the four bones of which it is composed. In the
young skull a suture may be seen extending on either side from the incisive
foramen to the interval between the lateral incisor and canine teeth, and
marking off the os incisivum
or premaxillary bone. At either posterior angle of
the hard palate is the greater palatine foramen, for the transmission of
the descending palatine vessels and anterior palatine nerve; and running
forward and medialward from it a groove, for the same
vessels and nerve. Behind the posterior palatine foramen is the pyramidal
process of the palatine bone, perforated by one or more lesser
palatine foramina, and marked by the commencement of a transverse ridge,
for the attachment of the tendinous expansion of the
Tensor veli palatini.
Projecting backward from the center of the posterior
border of the hard palate is the posterior nasal spine, for the
attachment of the Musculus uvulæ.
Behind and above the hard palate are the choanæ,
Behind the nasal cavities is the basilar portion of the occipital bone, presenting near its center the pharyngeal tubercle for the attachment of the fibrous raphé of the pharynx, with depressions on either side for the insertions of the Rectus capitis anterior and Longus capitis. At the base of the lateral pterygoid plate is the foramen ovale, for the transmission of the mandibular nerve, the accessory meningeal artery, and sometimes the lesser superficial petrosal nerve; behind this are the foramen spinosum which transmits the middle meningeal vessels, and the prominent spina angularis (sphenoidal spine), which gives attachment to the sphenomandibular ligament and the Tensor veli palatini. Lateral to the spina angularis is the mandibular fossa, divided into two parts by the petrotympanic fissure; the anterior portion, concave, smooth bounded in front by the articular tubercle, serves for the articulation of the condyle of the mandible; the posterior portion, rough and bounded behind by the tympanic part of the temporal, is sometimes occupied by a part of the parotid gland. Emerging from between the laminæ of the vaginal process of the tympanic part is the styloid process; and at the base of this process is the stylomastoid foramen, for the exit of the facial nerve, and entrance of the stylomastoid artery. Lateral to the stylomastoid foramen, between the tympanic part and the mastoid process, is the tympanomastoid fissure, for the auricular branch of the vagus. Upon the medial side of the mastoid process is the mastoid notch for the posterior belly of the Digastricus, and medial to the notch, the occipital groove for the occipital artery. At the base of the medial pterygoid plate is a large and somewhat triangular aperture, the foramen lacerum, bounded in front by the great wing of the sphenoid, behind by the apex of the petrous portion of the temporal bone, and medially by the body of the sphenoid and basilar portion of the occipital bone; it presents in front the posterior orifice of the pterygoid canal; behind, the aperture of the carotid canal. The lower part of this opening is filled up in the fresh state by a fibrocartilaginous plate, across the upper or cerebral surface of which the internal carotid artery passes. Lateral to this aperture is a groove, the sulcus tubæ auditivæ, between the petrous part of the temporal and the great wing of the sphenoid. This sulcus is directed lateralward and backward from the root of the medial pterygoid plate and lodges the cartilaginous part of the auditory tube; it is continuous behind with the canal in the temporal bone which forms the bony part of the same tube. At the bottom of this sulcus is a narrow cleft, the petrosphenoidal fissure, which is occupied, in the fresh condition, by a plate of cartilage. Behind this fissure is the under surface of the petrous portion of the temporal bone, presenting, near its apex, the quadrilateral rough surface, part of which affords attachment to the Levator veli palatini; lateral to this surface is the orifice of the carotid canal, and medial to it, the depression leading to the aquæductus cochleæ, the former transmitting the internal carotid artery and the carotid plexus of the sympathetic, the latter serving for the passage of a vein from the cochlea. Behind the carotid canal is the jugular foramen, a
large aperture, formed in front by the petrous portion of the temporal, and behind by the occipital; it is generally larger on the right than on the left side, and may be subdivided into three compartments. The anterior compartment transmits the inferior petrosal sinus; the intermediate, the glossopharyngeal, vagus, and accessory nerves; the posterior, the transverse sinus and some meningeal branches from the occipital and ascending pharyngeal arteries. On the ridge of bone dividing the carotid canal from the jugular foramen is the inferior tympanic canaliculus for the transmission of the tympanic branch of the glossopharyngeal nerve; and on the wall of the jugular foramen, near the root of the styloid process, is the mastoid canaliculus for the passage of the auricular branch of the vagus nerve. Extending forward from the jugular foramen to the foramen lacerum is the petrooccipital fissure occupied, in the fresh state, by a plate of cartilage. Behind the basilar portion of the occipital bone is the foramen magnum, bounded laterally by the occipital condyles, the medial sides of which are rough for the attachment of the alar ligaments. Lateral to each condyle is the jugular process which gives attachment to the Rectus capitis lateralis muscle and the lateral atlantooccipital ligament. The foramen magnum transmits the medulla oblongata and its membranes, the accessory nerves, the vertebral arteries, the anterior and posterior spinal arteries, and the ligaments connecting the occipital bone with the axis. The mid-points on the anterior and posterior margins of the foramen magnum are respectively termed the basion and the opisthion. In front of each condyle is the canal for the passage of the hypoglossal nerve and a meningeal artery. Behind each condyle is the condyloid fossa, perforated on one or both sides by the condyloid canal, for the transmission of a vein from the transverse sinus. Behind the foramen magnum is the median nuchal line ending above at the external occipital protuberance, while on either side are the superior and inferior nuchal lines; these, as well as the surfaces of bone between them, are rough for the attachment of the muscles which are enumerated on pages.
Side view of the skull.
viewed from the side the skull is seen to consist of the cranium above and
behind, and of the face below and in front. The cranium is somewhat ovoid in
shape, but its contour varies in different cases and depends largely on the
length and height of the skull and on the degree of prominence of the superciliary arches and frontal eminences. Entering into
its formation are the frontal, the parietal, the occipital, the temporal, and
the great wing of the sphenoid. These bones are joined to one another and to
the zygomatic by the following sutures: the zygomaticotemporal between the zygomatic
process of the temporal and the temporal process of the zygomatic;
the zygomaticofrontal uniting the zygomatic bone with the zygomatic
process of the frontal; the sutures surrounding the great wing of the sphenoid,
viz., the sphenozygomatic in front, the sphenofrontal and sphenoparietal
above, and the sphenosquamosal behind. The sphenoparietal suture varies in length in different skulls,
and is absent in those cases where the frontal articulates with the temporal squama. The point corresponding with the posterior end of
the sphenoparietal suture is named the pterion;
it is situated about
The squamosal suture arches backward from the pterion and connects the temporal squama with the lower border of the parietal: this suture is continuous behind with the short, nearly horizontal parietomastoid suture, which unites the mastoid process of the temporal with the region of the mastoid angle of the parietal. Extending from above downward and forward across the cranium are the coronal and lambdoidal sutures; the former connects the parietals with the frontal, the latter, the parietals with the occipital. The lambdoidal suture is continuous below with the occipitomastoid suture between the occipital and the mastoid portion of the temporal. In or near the last suture is the mastoid foramen, for the transmission of an emissary vein. The point of meeting of the parietomastoid, occipitomastoid, and lambdoidal sutures is known as the asterion. Immediately above the orbital margin is the superciliary arch, and, at a higher level, the frontal eminence. Near the center of the parietal bone is the parietal eminence. Posteriorly is the external occipital protuberance, from which the superior nuchal line may be followed forward to the mastoid process. Arching across the side of the cranium are the temporal lines, which mark the upper limit of the temporal fossa.
Temporal fossa formed by frontal squama and parietal bone. It bordered superiorly by temporal line, inferiorly – infratemporal srest and zygomatic arch. Temporal fossa contains temporal muscle.
Infratemporal fossa bordered by tuber maxillae, superiorly - infratemporal srest, medially it contimues into pterygopalatine fossa. Anteriorly infraemporal fossa communicates with orbit through inferior orbital fissura.
The Temporal Fossa (fossa temporalis).—The temporal fossa is bounded above and behind by the temporal lines, which extend from the zygomatic process of the frontal bone upward and backward across the frontal and parietal bones, and then curve downward and forward to become continuous with the supramastoid crest and the posterior root of the zygomatic arch. The point where the upper temporal line cuts the coronal suture is named the stephanion. The temporal fossa is bounded in front by the frontal and zygomatic bones, and opening on the back of the latter is the zygomaticotemporal foramen. Laterally the fossa is limited by the zygomatic arch, formed by the zygomatic and temporal bones; below, it is separated from the infratemporal fossa by the infratemporal crest on the great wing of the sphenoid, and by a ridge, continuous with this crest, which is carried backward across the temporal squama to the anterior root of the zygomatic process. In front and below, the fossa communicates with the orbital cavity through the inferior orbital or sphenomaxillary fissure. The floor of the fossa is deeply concave in front and convex behind, and is formed by the zygomatic, frontal, parietal, sphenoid, and temporal bones. It is traversed by vascular furrows; one, usually well-marked, runs upward above and in front of the external acoustic meatus, and lodges the middle temporal artery. Two others, frequently indistinct, may be observed on the anterior part of the floor, and are for the anterior and posterior deep temporal arteries. The temporal fossa contains the Temporalis muscle and its vessels and nerves, together with the zygomaticotemporal nerve.
The zygomatic arch is formed by the zygomatic process of the temporal and the temporal process of the zygomatic, the two being united by an oblique suture; the tendon of the Temporalis passes medial to the arch to gain insertion into the coronoid process of the mandible. The zygomatic process of the temporal arises by two roots, an anterior, directed inward in front of the mandibular fossa, where it expands to form the articular tubercle, and a posterior, which runs backward above the external acoustic meatus and is continuous with the supramastoid crest. The upper border of the arch gives attachment to the temporal fascia; the lower border and medial surface give origin to the Masseter.
Below the posterior root of the zygomatic arch is the elliptical orifice of the external acoustic meatus, bounded in front, below, and behind by the tympanic part of the temporal bone; to its outer margin the cartilaginous segment of the external acoustic meatus is attached. The small triangular area between the posterior root of the zygomatic arch and the postero-superior part of the orifice is termed the suprameatal triangle, on the anterior border of which a small spinous process, the suprameatal spine, is sometimes seen. Between the tympanic part and the articular tubercle is the mandibular fossa, divided into two parts by the petrotympanic fissure. The anterior and larger part of the fossa articulates with the condyle of the mandible and is limited behind by the external acoustic meatus: the posterior part sometimes lodges a portion of the parotid gland. The styloid process extends downward and forward for a variable distance from the lower part of the tympanic part, and gives attachment to the Styloglossus, Stylohyoideus, and Stylopharyngeus, and to the stylohyoid and stylomandibular ligaments. Projecting downward behind the external acoustic meatus is the mastoid process, to the outer surface of which the Sternocleidomastoideus, Splenius capitis, and Longissimus capitis are attached.
Left infratemporal fossa.
The Infratemporal Fossa (fossa infratemporalis; zygomatic fossa)—The infratemporal fossa is an irregularly shaped cavity, situated below and medial to the zygomatic arch. It is bounded, in front, by the infratemporal surface of the maxilla and the ridge which descends from its zygomatic process; behind, by the articular tubercle of the temporal and the spinal angularis of the sphenoid; above, by the great wing of the sphenoid below the infratemporal crest, and by the under surface of the temporal squama; below, by the alveolar border of the maxilla; medially, by the lateral pterygoid plate. It contains the lower part of the Temporalis, the Pterygoidei internus and externus, the internal maxillary vessels, and the mandibular and maxillary nerves. The foramen ovale and foramen spinosum open on its roof, and the alveolar canals on its anterior wall. At its upper and medial part are two fissures, which together form a T-shaped fissure, the horizontal limb being named the inferior orbital, and the vertical one the pterygomaxillary.
The inferior orbital fissure (fissura orbitalis inferior; sphenomaxillary fissure), horizontal in direction, opens into the lateral and back part of the orbit. It is bounded above by the lower border of the orbital surface of the great wing of the sphenoid; below, by the lateral border of the orbital surface of the maxilla and the orbital process of the palatine bone; laterally, by a small part of the zygomatic bone: 48 medially, it joins at right angles with the pterygomaxillary fissure. Through the inferior orbital fissure the orbit communicates with the temporal, infratemporal, and pterygopalatine fossæ; the fissure transmits the maxillary nerve and its zygomatic branch, the infraorbital vessels, the ascending branches from the sphenopalatine ganglion, and a vein which connects the inferior ophthalmic vein with the pterygoid venous plexus.
The pterygomaxillary fissure is vertical, and descends at right angles from the medial end of the preceding; it is a triangular interval, formed by the divergence of the maxilla from the pterygoid process of the sphenoid. It connects the infratemporal with the pterygopalatine fossa, and transmits the terminal part of the internal maxillary artery.
Norma Occipitalis.—When viewed from behind the cranium presents a more or less circular outline. In the middle line is the posterior part of the sagittal suture connecting the parietal bones; extending downward and lateralward from the hinder end of the sagittal suture is the deeply serrated lambdoidal suture joining the parietals to the occipital and continuous below with the parietomastoid and occipitomastoid sutures; it frequently contains one or more sutural bones. Near the middle of the occipital squama is the external occipital protuberance or inion, and extending lateralward from it on either side is the superior nuchal line, and above this the faintly marked highest nuchal line. The part of the squama above the inion and highest lines is named the planum occipitale, and is covered by the Occipitalis muscle; the part below is termed the planum nuchale, and is divided by the median nuchal line which runs downward and forward from the inion to the foramen magnum; this ridge gives attachment to the ligamentum nuchæ. The muscles attached to the planum nuchale are enumerated on p. 130. Below and in front are the mastoid processes, convex laterally and grooved medially by the mastoid notches. In or near the occipitomastoid suture is the mastoid foramen for the passage of the mastoid emissary vein.
Norma Frontalis—When viewed from the front the skull exhibits a somewhat oval outline, limited above by the frontal bone, below by the body of the mandible, and laterally by the zygomatic bones and the mandibular rami. The upper part, formed by the frontal squama, is smooth and convex. The lower part, made up of the bones of the face, is irregular; it is excavated laterally by the orbital cavities, and presents in the middle line the anterior nasal aperture leading to the nasal cavities, and below this the transverse slit between the upper and lower dental arcades.
The skull from the front.
Above, the frontal eminences stand out more or less prominently, and beneath these are the superciliary arches, joined to one another in the middle by the glabella. On and above the glabella a trace of the frontal suture sometimes persists; beneath it is the frontonasal suture, the mid-point of which is termed the nasion. Behind and below the frontonasal suture the frontal articulates with the frontal process of the maxilla and with the lacrimal. Arching transversely below the superciliary arches is the upper part of the margin of the orbit, thin and prominent in its lateral two-thirds, rounded in its medial third, and presenting, at the junction of these two portions, the supraorbital notch or foramen for the supraorbital nerve and vessels. The supraorbital margin ends laterally in the zygomatic process which articulates with the zygomatic bone, and from it the temporal line extends upward and backward. Below the frontonasal suture is the bridge of the nose, convex from side to side, concavo-convex from above downward, and formed by the two nasal bones supported in the middle line by the perpendicular plate of the ethmoid, and laterally by the frontal processes of the maxillæ which are prolonged upward between the nasal and lacrimal bones and form the lower and medial part of the circumference of each orbit. Below the nasal bones and between the maxillæ is the anterior aperture of the nose, pyriform in shape, with the narrow end directed upward. Laterally this opening is bounded by sharp margins, to which the lateral and alar cartilages of the nose are attached; below, the margins are thicker and curve medialward and forward to end in the anterior nasal spine. On looking into the nasal cavity, the bony septum which separates the nasal cavities presents, in front, a large triangular deficiency; this, in the fresh state, is filled up by the cartilage of the nasal septum; on the lateral wall of each nasal cavity the anterior part of the inferior nasal concha is visible. Below and lateral to the anterior nasal aperture are the anterior surfaces of the maxillæ, each perforated, near the lower margin of the orbit, by the infraorbital foramen for the passage of the infraorbital nerve and vessels. Below and medial to this foramen is the canine eminence separating the incisive from the canine fossa. Beneath these fossæ are the alveolar processes of the maxillæ containing the upper teeth, which overlap the teeth of the mandible in front. The zygomatic bone on either side forms the prominence of the cheek, the lower and lateral portion of the orbital cavity, and the anterior part of the zygomatic arch. It articulates medially with the maxilla, behind with the zygomatic process of the temporal, and above with the great wing of the sphenoid and the zygomatic process of the frontal; it is perforated by the zygomaticofacial foramen for the passage of the zygomaticofacial nerve. On the body of the mandible is a median ridge, indicating the position of the symphysis; this ridge divides below to enclose the mental protuberance, the lateral angles of which constitute the mental tubercles. Below the incisor teeth is the incisive fossa, and beneath the second premolar tooth the mental foramen which transmits the mental nerve and vessels. The oblique line runs upward from the mental tubercle and is continuous behind with the anterior border of the ramus. The posterior border of the ramus runs downward and forward from the condyle to the angle, which is frequently more or less everted.
The Interior of the Skull
Inner Surface of the Skull-cap.—The inner surface of the skull-cap is concave and presents depressions for the convolutions of the cerebrum, together with numerous furrows for the lodgement of branches of the meningeal vessels. Along the middle line is a longitudinal groove, narrow in front, where it commences at the frontal crest, but broader behind; it lodges the superior sagittal sinus, and its margins afford attachment to the falx cerebri. On either side of it are several depressions for the arachnoid granulations, and at its back part, the openings of the parietal foramina when these are present. It is crossed, in front, by the coronal suture, and behind by the lambdoidal, while the sagittal lies in the medial plane between the parietal bones.
Upper Surface of the Base of the Skull—The upper surface of the base of the skull or floor of the cranial cavity presents three fossæ, called the anterior, middle, and posterior cranial fossæ.
Anterior Fossa (fossa cranii anterior).—The floor of the anterior fossa is formed by the orbital plates of the frontal, the cribriform plate of the ethmoid, and the small wings and front part of the body of the sphenoid; it is limited behind by the posterior borders of the small wings of the sphenoid and by the anterior margin of the chiasmatic groove. It is traversed by the frontoethmoidal, sphenoethmoidal, and sphenofrontal sutures. Its lateral portions roof in the orbital cavities and support the frontal lobes of the cerebrum; they are convex and marked by depressions for the brain convolutions, and grooves for branches of the meningeal vessels. The central portion corresponds with the roof of the nasal cavity, and is markedly depressed on either side of the crista galli. It presents, in and near the median line, from before backward, the commencement of the frontal crest for the attachment of the falx cerebri; the foramen cecum, between the frontal bone and the crista galli of the ethmoid, which usually transmits a small vein from the nasal cavity to the superior sagittal sinus; behind the foramen cecum, the crista galli, the free margin of which affords attachment to the falx cerebri; on either side of the crista galli, the olfactory groove formed by the cribriform plate, which supports the olfactory bulb and presents foramina for the transmission of the olfactory nerves, and in front a slit-like opening for the nasociliary nerve. Lateral to either olfactory groove are the internal openings of the anterior and posterior ethmoidal foramina; the anterior, situated about the middle of the lateral margin of the olfactory groove, transmits the anterior ethmoidal vessels and the nasociliary nerve; the nerve runs in a groove along the lateral edge of the cribriform plate to the slit-like opening above mentioned; the posterior ethmoidal foramen opens at the back part of this margin under cover of the projecting lamina of the sphenoid, and transmits the posterior ethmoidal vessels and nerve. Farther back in the middle line is the ethmoidal spine, bounded behind by a slight elevation separating two shallow longitudinal grooves which support the olfactory lobes. Behind this is the anterior margin of the chiasmatic groove, running lateralward on either side to the upper margin of the optic foramen.
The Middle Fossa (fossa cranii media).—The middle fossa, deeper than the preceding, is narrow in the middle, and wide at the sides of the skull. It is bounded in front by the posterior margins of the small wings of the sphenoid, the anterior clinoid processes, and the ridge forming the anterior margin of the chiasmatic groove; behind, by the superior angles of the petrous portions of the temporals and the dorsum sellæ; laterally by the temporal squamæ, sphenoidal angles of the parietals, and great wings of the sphenoid. It is traversed by the squamosal, sphenoparietal, sphenosquamosal, and sphenopetrosal sutures.
The middle part of the fossa presents, in front, the chiasmatic groove and tuberculum sellæ; the chiasmatic groove ends on either side at the optic foramen, which transmits the optic nerve and ophthalmic artery to the orbital cavity. Behind the optic foramen the anterior clinoid process is directed backward and medialward and gives attachment to the tentorium cerebelli. Behind the tuberculum sellæ is a deep depression, the sella turcica, containing the fossa hypophyseos, which lodges the hypophysis, and presents on its anterior wall the middle clinoid processes. The sella turcica is bounded posteriorly by a quadrilateral plate of bone, the dorsum sellæ, the upper angles of which are surmounted by the posterior clinoid processes: these afford attachment to the tentorium cerebelli, and below each is a notch for the abducent nerve. On either side of the sella turcica is the carotid groove, which is broad, shallow, and curved somewhat like the italic letter f. It begins behind at the foramen lacerum, and ends on the medial side of the anterior clinoid process, where it is sometimes converted into a foramen (carotico-clinoid) by the union of the anterior with the middle clinoid process; posteriorly, it is bounded laterally by the lingula. This groove lodges the cavernous sinus and the internal carotid artery, the latter being surrounded by a plexus of sympathetic nerves.
Base of the skull. Upper surface.
The lateral parts of the middle fossa are of considerable depth, and support the temporal lobes of the brain. They are marked by depressions for the brain convolutions and traversed by furrows for the anterior and posterior branches of the middle meningeal vessels. These furrows begin near the foramen spinosum, and the anterior runs forward and upward to the sphenoidal angle of the parietal, where it is sometimes converted into a bony canal; the posterior runs lateralward and backward across the temporal squama and passes on to the parietal near the middle of its lower border. The following apertures are also to be seen. In front is the superior orbital fissure, bounded above by the small wing, below, by the great wing, and medially, by the body of the sphenoid; it is usually completed laterally by the orbital plate of the frontal bone. It transmits to the orbital cavity the oculomotor, the trochlear, the ophthalmic division of the trigeminal, and the abducent nerves, some filaments from the cavernous plexus of the sympathetic, and the orbital branch of the middle meningeal artery; and from the orbital cavity a recurrent branch from the lacrimal artery to the dura mater, and the ophthalmic veins. Behind the medial end of the superior orbital fissure is the foramen rotundum, for the passage of the maxillary nerve. Behind and lateral to the foramen rotundum is the foramen ovale, which transmits the mandibular nerve, the accessory meningeal artery, and the lesser superficial petrosal nerve. 50 Medial to the foramen ovale is the foramen Vesalii, which varies in size in different individuals, and is often absent; when present, it opens below at the lateral side of the scaphoid fossa, and transmits a small vein. Lateral to the foramen ovale is the foramen spinosum, for the passage of the middle meningeal vessels, and a recurrent branch from the mandibular nerve. Medial to the foramen ovale is the foramen lacerum; in the fresh state the lower part of this aperture is filled up by a layer of fibrocartilage, while its upper and inner parts transmit the internal carotid artery surrounded by a plexus of sympathetic nerves. The nerve of the pterygoid canal and a meningeal branch from the ascending pharyngeal artery pierce the layer of fibrocartilage. On the anterior surface of the petrous portion of the temporal bone are seen the eminence caused by the projection of the superior semicircular canal; in front of and a little lateral to this a depression corresponding to the roof of the tympanic cavity; the groove leading to the hiatus of the facial canal, for the transmission of the greater superficial petrosal nerve and the petrosal branch of the middle meningeal artery; beneath it, the smaller groove, for the passage of the lesser superficial petrosal nerve; and, near the apex of the bone, the depression for the semilunar ganglion and the orifice of the carotid canal.
The Posterior Fossa (fossa cranii posterior).—The posterior fossa is the largest and deepest of the three. It is formed by the dorsum sellæ and clivus of the sphenoid, the occipital, the petrous and mastoid portions of the temporals, and the mastoid angles of the parietal bones; it is crossed by the occipitomastoid and the parietomastoid sutures, and lodges the cerebellum, pons, and medulla oblongata. It is separated from the middle fossa in and near the median line by the dorsum sellæ of the sphenoid and on either side by the superior angle of the petrous portion of the temporal bone. This angle gives attachment to the tentorum cerebelli, is grooved for the superior petrosal sinus, and presents at its medial end a notch upon which the trigeminal nerve rests. The fossa is limited behind by the grooves for the transverse sinuses. In its center is the foramen magnum, on either side of which is a rough tubercle for the attachment of the alar ligaments; a little above this tubercle is the canal, which transmits the hypoglossal nerve and a meningeal branch from the ascending pharyngeal artery. In front of the foramen magnum the basilar portion of the occipital and the posterior part of the body of the sphenoid form a grooved surface which supports the medulla oblongata and pons; in the young skull these bones are joined by a synchondrosis. This grooved surface is separated on either side from the petrous portion of the temporal by the petro-occipital fissure, which is occupied in the fresh state by a plate of cartilage; the fissure is continuous behind with the jugular foramen, and its margins are grooved for the inferior petrosal sinus. The jugular foramen is situated between the lateral part of the occipital and the petrous part of the temporal. The anterior portion of this foramen transmits the inferior petrosal sinus; the posterior portion, the transverse sinus and some meningeal branches from the occipital and ascending pharyngeal arteries; and the intermediate portion, the glossopharyngeal, vagus, and accessory nerves. Above the jugular foramen is the internal acoustic meatus, for the facial and acoustic nerves and internal auditory artery; behind and lateral to this is the slit-like opening leading into the aquæductus vestibuli, which lodges the ductus endolymphaticus; while between these, and near the superior angle of the petrous portion, is a small triangular depression, the remains of the fossa subarcuata, which lodges a process of the dura mater and occasionally transmits a small vein. Behind the foramen magnum are the inferior occipital fossæ, which support the hemispheres of the cerebellum, separated from one another by the internal occipital crest, which serves for the attachment of the falx cerebelli, and lodges the occipital sinus. The posterior fossæ are surmounted by the deep grooves for the transverse sinuses. Each of these channels, in its passage to the jugular foramen, grooves the occipital, the mastoid angle of the parietal, the mastoid portion of the temporal, and the jugular process of the occipital, and ends at the back part of the jugular foramen. Where this sinus grooves the mastoid portion of the temporal, the orifice of the mastoid foramen may be seen; and, just previous to its termination, the condyloid canal opens into it; neither opening is constant.
Theme 2. Orbit. Nasal cavity
Orbit has a superior, inferior, lateral and medial walls. Upper wall formed by frontal bone and sphenoid lesser alae. Lower wall composed by maxilla, zygomatic and palatine bones. Lateral wall formed by zygomatic bone and sphenoid greater alae. Medial wall consists of frontal process of the maxilla, lacrimal bone, orbital plate of the ethmoidal bone and sphenoid body.
Orbit opens out that bordered supraorbital and infraorbital margins. Superior orbital fissure positioned between upper and lateral walls, inferior orbital fissure - lower and lateral walls.
Laterally one can find fossa for lacrimal gland. Infraorbital sulcus and canal are on the lower wall. Canal opens by infraorbital foramen in canine fossa on facial surface of the skull. Anterior and posterior ethmoid foramen are on medial orbital wall. Orbit communicates with skull cavity by the optic canals and nasal cavity - through nasolacrimal canal (on medial orbital wall).
The Orbits (orbitæ)—The orbits are two quadrilateral pyramidal cavities, situated at the upper and anterior part of the face, their bases being directed forward and lateralward, and their apices backward and medialward, so that their long axes, if continued backward, would meet over the body of the sphenoid. Each presents for examination a roof, a floor, a medial and a lateral wall, a base, and an apex.
Medial wall of left orbit.
The roof is concave, directed downward, and slightly forward, and formed in front by the orbital plate of the frontal; behind by the small wing of the sphenoid. It presents medially the trochlear fovea for the attachment of the cartilaginous pulley of the Obliquus oculi superior; laterally, the lacrimal fossa for the lacrimal gland; and posteriorly, the suture between the frontal bone and the small wing of the sphenoid.
The floor is directed upward and lateralward, and is of less extent than the roof; it is formed chiefly by the orbital surface of the maxilla; in front and laterally, by the orbital process of the zygomatic bone, and behind and medially, to a small extent, by the orbital process of the palatine. At its medial angle is the upper opening of the nasolacrimal canal, immediately to the lateral side of which is a depression for the origin of the Obliquus oculi inferior. On its lateral part is the suture between the maxilla and zygomatic bone, and at its posterior part that between the maxilla and the orbital process of the palatine. Running forward near the middle of the floor is the infraorbital groove, ending in front in the infraorbital canal and transmitting the infraorbital nerve and vessels.
The medial wall is nearly vertical, and is formed from before backward by the frontal process of the maxilla, the lacrimal, the lamina papyracea of the ethmoid, and a small part of the body of the sphenoid in front of the optic foramen. Sometimes the sphenoidal concha forms a small part of this wall.It exhibits three vertical sutures, viz., the lacrimomaxillary, lacrimoethmoidal, and sphenoethmoidal. In front is seen the lacrimal groove, which lodges the lacrimal sac, and behind the groove is the posterior lacrimal crest, from which the lacrimal part of the Orbicularis oculi arises. At the junction of the medial wall and the roof are the frontomaxillary, frontolacrimal, frontoethmoidal, and sphenofrontal sutures. The point of junction of the anterior border of the lacrimal with the frontal is named the dacryon. In the frontoethmoidal suture are the anterior and posterior ethmoidal foramina, the former transmitting the nasociliary nerve and anterior ethmoidal vessels, the latter the posterior ethmoidal nerve and vessels.
The lateral wall, directed medialward and forward, is formed by the orbital process of the zygomatic and the orbital surface of the great wing of the sphenoid; these are united by the sphenozygomatic suture which terminates below at the front end of the inferior orbital fissure. On the orbital process of the zygomatic bone are the orbital tubercle (Whitnall) and the orifices of one or two canals which transmit the branches of the zygomatic nerve. Between the roof and the lateral wall, near the apex of the orbit, is the superior orbital fissure. Through this fissure the oculomotor, the trochlear, the ophthalmic division of the trigeminal, and the abducent nerves enter the orbital cavity, also some filaments from the cavernous plexus of the sympathetic and the orbital branches of the middle meningeal artery. Passing backward through the fissure are the ophthalmic vein and the recurrent branch from the lacrimal artery to the dura mater. The lateral wall and the floor are separated posteriorly by the inferior orbital fissure which transmits the maxillary nerve and its zygomatic branch, the infraorbital vessels, and the ascending branches from the sphenopalatine ganglion.
The base of the orbit, quadrilateral in shape, is formed above by the supraorbital arch of the frontal bone, in which is the supraorbital notch or foramen for the passage of the supraorbital vessels and nerve; below by the zygomatic bone and maxilla, united by the zygomaticomaxillary suture; laterally by the zygomatic bone and the zygomatic process of the frontal joined by the zygomaticofrontal suture; medially by the frontal bone and the frontal process of the maxilla united by the frontomaxillary suture.
The apex, situated at the back of the orbit, corresponds to the optic foramen 49 a short, cylindrical canal, which transmits the optic nerve and ophthalmic artery.
It will thus be seen that there are nine openings communicating with each orbit, viz., the optic foramen, superior and inferior orbital fissures, supraorbital foramen, infraorbital canal, anterior and posterior ethmoidal foramina, zygomatic foramen, and the canal for the nasolacrimal duct.
Bony cavity of the nose opens forward by piriform aperture, backward connects nasopharynx through choanae. Nasal cavity has a superior, inferior and medial walls and it is separated by bony septum into right and left halves.
Lateral wall formed by:
· nasal bone
· frontal process of the maxilla
· lacrimal bone
· ethmoidal labyrinth
· perpendicular plate of the palatine bone
· medial plate of the pterygoid process (sphenoid bone)
Upper wall (roof) formed by frontal bone and cribriform plate (ethmoid bone). Lower wall composed by bony palatine (alveolar process of the maxilla and horizontal plate of the palatine bone).
Bony nasal septum consists of perpendicular plate (ethmoid bone) and vomer.
Superior nasal meatus passes between upper and middle nasal conchae and communicates with sphenoid sinus through sphenoethmoid recess. Posterior ethmoid cells open into superior nasal meatus
Middle nasal meatus runs between middle and lower nasal conchae and communicates with frontal (through ethmoid infundibulum) and maxillary (Haimory) sinus (through semilunar hiatus), and with anterior and middle ethmoid cells.
Inferior nasal meatus passes between lower nasal concha and bony palate; nasolacrimal canal and incisive canal open in it.
Horizontal section of nasal and orbital cavities.)
Sagittal section of skull.
The nasal cavities are two irregular spaces, situated one on either side of the middle line of the face, extending from the base of the cranium to the roof of the mouth, and separated from each other by a thin vertical septum. They open on the face through the pear-shaped anterior nasal aperture, and their posterior openings or choanæ communicate, in the fresh state, with the nasal part of the pharynx. They are much narrower above than below, and in the middle than at their anterior or posterior openings: their depth, which is considerable, is greatest in the middle. They communicate with the frontal, ethmoidal, sphenoidal, and maxillary sinuses. Each cavity is bounded by a roof, a floor, a medial and a lateral wall.
The roof is horizontal in its central part, but slopes downward in front and behind; it is formed in front by the nasal bone and the spine of the frontal; in the middle, by the cribriform plate of the ethmoid; and behind, by the body of the sphenoid, the sphenoidal concha, the ala of the vomer and the sphenoidal process of the palatine bone. In the cribriform plate of the ethmoid are the foramina for the olfactory nerves, and on the posterior part of the roof is the opening into the sphenoidal sinus.
Medial wall of left nasal fossa.
The floor is flattened from before backward and concave from side to side. It is formed by the palatine process of the maxilla and the horizontal part of the palatine bone; near its anterior end is the opening of the incisive canal.
Roof, floor, and lateral wall of left nasal cavity.
The medial wall (septum nasi) is frequently deflected to one or other side, more often to the left than to the right. It is formed, in front, by the crest of the nasal bones and frontal spine; in the middle, by the perpendicular plate of the ethmoid; behind, by the vomer and the rostrum of the sphenoid; below, by the crest of the maxillæ and palatine bones. It presents, in front, a large, triangular notch, which receives the cartilage of the septum; and behind, the free edge of the vomer. Its surface is marked by numerous furrows for vessels and nerves and by the grooves for the nasopalatine nerve, and is traversed by sutures connecting the bones of which it is formed.
The lateral wall is formed, in front, by the frontal process of the maxilla and by the lacrimal bone; in the middle, by the ethmoid, maxilla, and inferior nasal concha; behind, by the vertical plate of the palatine bone, and the medial pterygoid plate of the sphenoid. On this wall are three irregular anteroposterior passages, termed the superior, middle, and inferior meatuses of the nose. The superior meatus, the smallest of the three, occupies the middle third of the lateral wall. It lies between the superior and middle nasal conchæ; the sphenopalatine foramen opens into it behind, and the posterior ethmoidal cells in front. The sphenoidal sinus opens into a recess, the sphenoethmoidal recess, which is placed above and behind the superior concha. The middle meatus is situated between the middle and inferior conchæ, and extends from the anterior to the posterior end of the latter. The lateral wall of this meatus can be satisfactorily studied only after the removal of the middle concha. On it is a curved fissure, the hiatus semilunaris, limited below by the edge of the uncinate process of the ethmoid and above by an elevation named the bulla ethmoidalis; the middle ethmoidal cells are contained within this bulla and open on or near to it. Through the hiatus semilunaris the meatus communicates with a curved passage termed the infundibulum, which communicates in front with the anterior ethmoidal cells and in rather more than fifty per cent. of skulls is continued upward as the frontonasal duct into the frontal air-sinus; when this continuity fails, the frontonasal duct opens directly into the anterior part of the meatus. Below the bulla ethmoidalis and hidden by the uncinate process of the ethmoid is the opening of the maxillary sinus (ostium maxillare); an accessory opening is frequently present above the posterior part of the inferior nasal concha. The inferior meatus, the largest of the three, is the space between the inferior concha and the floor of the nasal cavity. It extends almost the entire length of the lateral wall of the nose, is broader in front than behind, and presents anteriorly the lower orifice of the nasolacrimal canal.
The Anterior Nasal Aperture is a heart-shaped or pyriform opening, whose long axis is vertical, and narrow end upward; in the recent state it is much contracted by the lateral and alar cartilages of the nose. It is bounded above by the inferior borders of the nasal bones; laterally by the thin, sharp margins which separate the anterior from the nasal surfaces of the maxillæ; and below by the same borders, where they curve medialward to join each other at the anterior nasal spine.
The choanæ are each bounded above by the under surface of the body of the sphenoid and ala of the vomer; below, by the posterior border of the horizontal part of the palatine bone; laterally, by the medial pterygoid plate; they are separated from each other by the posterior border of the vomer.
Peculiarities of foetal skull
Anterior fontanelle positioned between unfused halves of the frontal bones. It is overgrown until 1 year old age. Posterior fontanelle located between parietal and occipital bones. It is overgrown till 2-3 months age. Mastoid fontanelle (paired) located between parietal, occipital and temporal bones. It is overgrown in last days before birth or during first 2-3 months. Sphenoid fontanelle (paired) located between frontal, parietal, sphenoid and temporal bones. It is overgrown in last week before birth or during first 2-3 months of life.
Differences in the Skull Due to AgeAt birth the skull is large in proportion to the other parts of the skeleton, but its facial portion is small, and equals only about one-eighth of the bulk of the cranium as compared with one-half in the adult. The frontal and parietal eminences are prominent, and the greatest width of the skull is at the level of the latter; on the other hand, the glabella, superciliary arches, and mastoid processes are not developed. Ossification of the skull bones is not completed, and many of them, e. g., the occipital, temporals, sphenoid, frontal, and mandible, consist of more than one piece. Unossified membranous intervals, termed fontanelles, are seen at the angles of the parietal bones; these fontanelles are six in number: two, an anterior and a posterior, are situated in the middle line, and two, an antero-lateral and a postero-lateral, on either side.
The anterior or bregmatic
fontanelle is the largest, and is placed at the
junction of the sagittal, coronal, and frontal sutures; it is lozenge-shaped,
and measures about
extension of the bones which surround them, but sometimes they are the sites of separate ossific centers which develop into sutural bones. The posterior and lateral fontanelles are obliterated within a month or two after birth, but the anterior is not completely closed until about the middle of the second year.
Skull at birth, showing frontal and occipital fonticuli.
The smallness of the face at birth is mainly accounted for by the rudimentary condition of the maxillæ and mandible, the non-eruption of the teeth, and the small size of the maxillary air sinuses and nasal cavities. At birth the nasal cavities lie almost entirely between the orbits, and the lower border of the anterior nasal aperture is only a little below the level of the orbital floor. With the eruption of the deciduous teeth there is an enlargement of the face and jaws, and these changes are still more marked after the second dentition.
The skull grows rapidly from birth to the seventh year, by which time the foramen magnum and petrous parts of the temporals have reached their full size and the orbital cavities are only a little smaller than those of the adult. Growth is slow from the seventh year until the approach of puberty, when a second period of activity occurs: this results in an increase in all directions, but it is especially marked in the frontal and facial regions, where it is associated with the development of the air sinuses.
Obliteration of the sutures of the vault of the skull takes place as age advances. This process may commence between the ages of thirty and forty, and is first seen on the inner surface, and some ten years later on the outer surface of the skull. The dates given are, however, only approximate, as it is impossible to state with anything like accuracy the time at which the sutures are closed. Obliteration usually occurs first in the posterior part of the sagittal suture, next in the coronal, and then in the lambdoidal.
In old age the skull generally becomes thinner and lighter, but in a small proportion of cases it increases in thickness and weight, owing to an hypertrophy of the inner table. The most striking feature of the old skull is the diminution in the size of the maxillæ and mandible consequent on the loss of the teeth and the absorption of the alveolar processes. This is associated with a marked reduction in the vertical measurement of the face and with an alteration in the angles of the mandible.
Skull at birth, showing sphenoidal and mastoid fonticuli.
Sexual Differences in the Skull Until the age of puberty there is little difference between the skull of the female and that of the male. The skull of an adult female is, as a rule, lighter and smaller, and its cranial capacity about 10 per cent. less, than that of the male. Its walls are thinner and its muscular ridges less strongly marked; the glabella, superciliary arches, and mastoid processes are less prominent, and the corresponding air sinuses are small or rudimentary. The upper margin of the orbit is sharp, the forehead vertical, the frontal and parietal eminences prominent, and the vault somewhat flattened. The contour of the face is more rounded, the facial bones are smoother, and the maxillæ and mandible and their contained teeth smaller. From what has been said it will be seen that more of the infantile characteristics are retained in the skull of the adult female than in that of the adult male. A well-marked male or female skull can easily be recognized as such, but in some cases the respective characteristics are so indistinct that the determination of the sex may be difficult or impossible.
Age changes in the face
Deciduous teeth usually begin to erupt in infants of approximately 6 months of age. The body of the mandible elongates particularly posterior to the mental foramen, to accommodate the development and then the bearing of eight secondary (permanent) teeth, which begin to erupt during the 6th year of life. Eruption of these permanent teeth is not complete until early adulthood. Rapid growth of the face during infancy and early childhood coincides with the eruption of primary teeth. Vertical growth of the upper face results mainly from dentoalveolar development. These changes are more marked after the secondary teeth erupt. Following complete loss of teeth in old age (or younger if care is neglected), the alveoli begin to fill in with bone and the alveolar processes begin to resorb. Concurrent enlargement of the frontal and facial regions is associated with the increase in the size of the paranasal sinuses – air-filled extensions of the nasal cavities in certain cranial bones. Most paranasal sinuses are rudimentary or absent at birth and develop during 1 – 2 year. Growth of the paranasal sinuses is important in altering the shape of the face and in adding resonance to the voice.
Obliteration of the cranial sutures
The obliteration of sutures between the bones of the calvaria usually begins between the ages of 30 and 40 on the internal surface and approximately 10 years later on the external surface. Obliteration of sutures usually begins at the bregma and continues seguentially in the sagittal, coronal, and lambdoid sutures.
Age changes in the skull
As people age the skull bones normally become progressivey thinner and lighter, and the diploe gradually become filled with a gray gelatinous material. In these individuals the bone marrow has lost its blood cells and fat, giving it a gelatinous appearance.
Skulls vary in size and shape, and the term craniology is applied to the study of these variations. The capacity of the cranial cavity constitutes a good index of the size of the brain which it contained, and is most conveniently arrived at by filling the cavity with shot and measuring the contents in a graduated vessel. Skulls may be classified according to their capacities as follows:
1. Microcephalic, with a capacity of less then 1350 c. cm. , those of native Australians and Andaman Islanders.
2. Mesocephalic, with a capacity of less then 1350 c. cm. to 1450 c. cm. , those of African and Chinese.
3. Megacefalic, with a capacity of over 1450 cm2 – e.g. , those of Europeans, Japanese and Eskimos.
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