The exterior of the skull

The skull, when viewed from above, presents an oval outline; the posterior part is broader than the anterior. The bones seen in this view are the frontal, parietals and the interparietal portion of the occipital. In a skull of average width the zygomata come into view, but in very broad skulls they are obscured.

The sutures of the vertex are:

The metopic, which is, in most skulls, merely a median fissure in the frontal bone just above the glabella; occasionally it involves the whole length of the bone. It is due to the persistence of the fissure normally separating the two halves of the bone in the infant.
The sagittal is situated between the two parietals and extends from the bregma to the lambda.
The coronal lies between the frontal and parietals and extends from pterion to pterion.
The lambdoid is formed by the ]Darietals and interparietal portion of the occipital. It extends from asterion to asterion.
The occipital suture is only present when the interparietal exists as a separate element.
The more important regions are:
The bregma, which indicates the situation of the anterior fontanelle and marks the confluence of the coronal, sagittal and, when present, the metopic sutures.
The lambda, where the sagittal enters the lambdoid suture; it marks the situation of the posterior fontanelle.
The obelion, a little anterior to the lambda, is usually indicated by a median or two lateral foramina. It indicates the spot where the sagittal suture first suffers obliteration.

Viewed from behind, the skull appears irregularly globular; the inferior part of its circumference being somewhat flattened. The limits of the flattened portion are indicated by the mastoid processes.

The centre is occupied by the occipital protuberance; this, with the occipital crest and the three pairs of nuchal lines, give to the lower half a rough and uneven appearance. The sutures in this view are the terminations of the sagittal, lambdoidal and, when present, the occipital suture.

The occipital point is the most posterior part of the skull and is exactly opposite the ophryon.

The inion corresponds to the external occipital protuberance.

The lateral aspect of the skull is very uneven; it presents three recesses or fossae and below by the zygoma.

The temporal ridge begins at the external angular process of the frontal bone and curves upwards and backwards to cross the frontal and parietal bones; it then

The Skull. (Norma lateralis.)

descends along the mastoid portion of the temporal bone to become continuous with the upper border of the zygoma. In many skulls this ridge is double. The lower ridge gives origin to the temjwml muscle. The upper is the least constant; it diverges from the lower ridge as it approaches the coronal suture. At the middle of the parietal bone the two ridges are often ten milhmetres apart. This ridge gives attachment to the temporal fascia. The fossa is almost entirely occupied by the temporal muscle.

The zygomatic fossa is limited anteriorly by the zygomatic surface of the maxilla; internally by the external pterygoid plate; externally by the zygomatic arch and the ramus of the mandible; and posteriorly by a line drawn from the foramen spinosum to the zygomatic tubercle. The outer surface of the greater wing of the sphenoid behind the pterygoid ridge and a small piece of the squamosal form part of the upper boundary of the fossa.

The chief objects of interest in this region are:- The spheno-maxillary and pterygo-maxillary fissures, the pterygoid ridge on the sphenoidal wing, the fora- men ovale, foramen spinosum and the articular eminence of the squamosal.

The spheno-maxillary fissure is horizontal in position and lies between the orbital border of the maxilla and the greater wing of the sphenoid; externally it is completed usually by the malar; frequently the sphenoid will join the maxilla and exclude the malar bone from the fissure; internally it is terminated by the zygomatic surface of the orbital process of the palate bone. Through this fissure the orbital, spheno-maxillary and zygomatic fossae communicate. The zygomatic fossa lodges the temporal, external pterygoid and internal pterygoicl muscles.

The pterygo-maxillary fissure forms a right angle with the preceding. It is situated between the maxilla and the anterior border of the external pterygoid process. At its lower angle the external pterygoid plate occasionally articulates

A Section of the Skull, showing the Inner Wall of the Orbit, the Base of the Antrum and the Spheno-maxillary Fossa.

with the maxilla. The pterygo-maxillary fissure leads from the zygomatic fossa directly into the spheno-maxillary fossa, a small space shaped like an inverted pyramid, situated between the maxilla and the roots of the pterygoid processes. The roof of this fossa is formed by the under surface of the greater wing of the sphenoid. The anterior boundaries are a small portion of the zygomatic surface of the maxilla and the orbital process of the palate; posteriorly it has the roots of the pterygoid processes and the low^er part of the orbital surface of the greater wing of the sphenoid; and internally the vertical plate of the palate bone. The apex of the pyramid leads into the posterior palatine canal. The inner wall presents the spheno-palatine foramen which leads into the nasal fossa. The posterior wall has three openings in the following order, from without inwards and from above downwards: the foramen rotundum, Vidian canal and pterygo-paiatine canal. Anteriorly it communicates with the orbit by the spheno-maxillary fissure; and externally the pterygo-maxillary fissure leads into the zygomatic fossa.

This fossa is mainly of interest on account of its relation to the spheno-palatine (Meckel's) ganglion. The various foramina and canals connected with the fossa serve for the transmission of the nerves connected with this ganglion and the M terminal branches of the internal maxillary artery.
In addition to the fossae, the lateral region presents the glenoid fossa with its articular eminence, the external auditory meatus, the mastoid and styloid processes and the following sutures:
The spheno-parietal, which lies between the greater wing of the sphenoid and the anterior inferior angle of the parietal.
The squamous is formed by the squamosal overlapping the lower border of the parietal.
The parieto-mastoid, which lies between the posterior inferior angle of the parietal and the mastoid portion of the petrosal.
The zygomatic suture is formed by the union of the zygoma with the malar bone.
The squamo-sphenoidal is situated between the anterior border of the squamosal and the greater wing of the sphenoid.
The spheno-malar suture is formed by the orbital process of the malar and the malar ridge on the greater wing of the sphenoid. Near its middle the suture is perforated by the spheno-malar foramen, which allows the temporal branch of the orbital nerve and a branch of the lachrymal artery to escape from the orbit. This foramen in some adult skulls is complete in the malar.
The fronto-squamosal is an occasional suture; when it is present, the anterior inferior angle of the parietal is excluded from the greater wing of the sphenoid.

Hard Palate of a Child Five Years old.

The more important regions are:

The pterion, which marks the situation of the anterior lateral fontanelle, is the meeting-place of the coronal, squamous, spheno-parietal, squamo-sphenoidal and the fronto-squamosal sutures. Frequently it is occupied in the adult by the epipteric ossicle.
The asterion indicates the situation of the posterior lateral fontanelle and marks the confluence of the squamosal, parieto-mastoid, lambdoid, the occipito-mastoid and occasionally the occipital sutures. Sometimes it is occupied by a Wormian bone.
The stephanion is the spot where the superior temporal ridge cuts the coronal suture.
The auricular point is the centre of the external auditory meatus. The base of the skull is very irregular and extends from the incisor teeth to the occipital protuberance. Laterally it is limited by the zygomatic arches. Anteriorly it presents the hard palate. "When the skull is inverted the hard palate stands at a higher level than the rest; it is bounded anteriorly and laterally by the alveolar ridges containing the teeth. The bones appearing in the intermediate space are the pre-maxillary and palatine portions of the maxillae and the horizontal plates of the palate bones. The bone is rough for the attachment of the muco-periosteum.

The following points are readily recognized:

The meso-palatine suture commences at the alveolar point, traverses the anterior palatine fossa and terminates at the posterior nasal spine.
The transverse palatine suture between the palate bones and palatine processes of the maxillae.
In young skulls the maxillo-premaxillary sutures and behind the incisor teeth four small openings known as the gubernacular canals.
The anterior palatine fossa containing the termination of four canals: two small orifices, foramina of Scarpa, situated one behind the other in the mesopalatine suture; and two larger openings, the foramina of Stenson. Scarpa's jforamina transmit the naso-palatine nerves; Stenson's are in relation with Jacob- son's organs.
At the posterior angles of the hard palate are the posterior palatine foramina, through which the posterior palatine vessels and the anterior palatine nerves emerge on to the palate; a thin lip of bone separates them from the accessory palatine foramina for the posterior palatine nerves. The accessory foramina are in the tuberosity of the palate bone.
The hamular process of the internal pterygoid plate is the most posterior limit of the hard palate.
At the posterior extremity of each alveolar ridge is the tuberosity of the maxilla. Between the tuberosities of the maxilla and the palate bone are a few minute foramina (variable in number and not always present), the external palatine canals for the external palatine nerves.
Behind the hard palate are the posterior nares, separated from each other by the vomer. Each is bounded externally by the internal pterygoid plate; below by the horizontal plate of the palate bone; above by the under surface of the body of the sphenoid, with the ala of the vomer and a portion of the sphenoidal process of the palate bone.

External to the nares there is on each side a vertical fossa lying between the pterygoid plates. It extends upwards to the under surface of the greater wings of the sphenoid; it is completed anteriorly by the coalescence of the pterygoid plates and below by the tuberosity of the palate bone. It contains the following points of interest:

An elongated furrow, the scaphoid fossa, for the tensor palati muscle.
The general cavity of the pterygoid fossa which lodges the tensor palati and internal pterygoid muscles.
Frequently there is a notch in the external pterygoid plate close beside the foramen ovale.
The posterior termination of the Vidian canal.

If a line be drawn across the skull base from one zygomatic tubercle to the other, it will fall immediately behind the external pterygoid plate and bisect the foramen spinosum on each side. A second transverse line, drawn across the opisthion or posterior margin of the foramen magnum, will fall behind the mastoid processes. The space between these imaginary lines may be called the sub-cranial region; that behind the second line the sub-occipital region. In addition to these there is a lateral space anterior to the first line known as the zygomatic region. Each will require separate consideration.

The Skull. (Norma basilaris.)

The sub-cranial region is formed by the following bones:

In the centre, the under surface of the bodies of the sphenoid and occipital bones. Laterally, the petrosal, a small piece of the greater wing of the sphenoid and of the squamosal and part of the occipital.

It presents the following points in the middle line for study:

The pharyngeal tubercle.
The foramen magnum and the occipital condyles. The most anterior point of the foramen is termed the basion and the most posterior point the opisthion.

The Skull. (Norma facialis.)

On each side will be seen:

The anterior condyloid foramen for the hypoglossal nerve and a meningeal branch of the ascending pharyngeal artery.
The posterior condyloid fossa with the posterior condyloid foramen (this foramen is not constant).
The sphenotic (middle lacerated) foramen and the orifice of the Vidian canal. The canalis musculo-tubarius for the tensor tympani muscle and Eustachian tube.
The carotid canal.
Aqueductus cochleae, or ductus perilymphaticus.
The jugular foramen and fossa for the giosso-pharyngeal, vagus and spinal accessory nerves, the internal jugular vein and a meningeal branch of the ascending pharyngeal artery.
The tympanic canaliculus for Jacobson's nerve. (Tympanic of glosso-pharyngeal.)

The Skull. (Norma facialis.)

The alar spine of the sphenoid; this is sometimes fifteen millimetres in length.

The glenoid fossa with the Glaserian fissure. This- lodges the slender process of the malleus, the tympanic twig of the internal maxillary artery. A small passage beside it, the canal of Huguier, conducts the chorda tympani nerve from the tympanum.

The external auditory meatus.

The auricular fissure for the tympanic branch of the vagus. The tympanic plate and vaginal process. The styloid process.

The stylo-mastoid foramen for the stylo-mastoid artery and the exit of the facial nerve.

The mastoid process with the digastric and occipital grooves.

The sub-occipital region presents chiefly muscular ridges. They are the superior, middle and inferior nuchal lines, with the external occipital protuberance and the external occipital crest. Behind the mastoid process is an opening of variable size, the mastoid foramen; a branch of the occipital artery enters and a vein from the lateral sinus issues from this foramen.

The anterior aspect of the skull is oval in outline, but presents a very irregular surface. Its upper portion, or forehead, presents the frontal eminences and super- ciliary ridges. In the middle line is the prominence formed by the nasal bones, with a deep pyramidal recess, the orbits, on each side. Below the nasal bones are the entrances to the nasal sinuses and the various recesses connected with them. The teeth form a conspicuous feature in this view of the skull, the outline of which is completed by the mandible.

The bones visible in this view of the skull are: the frontal, nasals, lachrymals orbital surfaces of the lesser and the greater wings and a portion of the body of the sphenoid, the ossa plana of ethmoid and the orbital processes of the palate bones, the malars, maxillae, inferior turbinals and the mandible.

The foramina are: the supraorbital, infraorbital, optic, temporal and mental; the lachrymal duct; the malar and ethmoidal canals; and the spheno-maxillary and sphenoidal fissures.

The orbits are two cavities of pyramidal shape, which lodge the eyeball and its associated muscles, nerves and vessels. The apex of each orbit corresponds ta the optic foramen, a circular orifice which transmits the optic nerve and ophthalmic artery. The base looks forwards and outwards. It is formed by the frontal bone above, the nasal process of the maxilla on the inner side, the malar bone externally and below by the malar and body of the maxilla. The following points are seen around the base: The suture between the external angular process of the frontal bone and the malar; the supraorbital notch (sometimes a complete foramen); and the suture between the frontal bone and the nasal process of the maxilla; and in the inferior segment of the circumference is the malo-maxillary suture. Occasionally, the infraorbital foramen opens by a narrow fissure into the orbit.

The roof of the orbit is formed mainly by the orbital plate of the frontal bone and completed posteriorly by the lesser wing of the sphenoid. At the outer angle it presents the lachrymal fossa for the lachrymal gland and at the inner angle a depression for the pulley of the su])erior oblique muscle.

The floor is formed by the orbital plate of the maxilla, the orbital process of the malar and the orbital process of the palate bone. At its inner angle it presents the lachrymal canal and near this a depression for the origin of the inferior oblique muscle. The floor has a furrow for the infraorbital artery and the superior maxillary di\usion of the fifth nerve. The furrow terminates anteriorly in the infraorbital canal, through which the infraorbital nerve and artery emerge on the face. Near the commencement of the canal a narrow passage, the anterior dental canal, runs forwards and downwards in the anterior wall of the antrum; it conducts nerves to the incisor and canine teeth.

The outer wall is very oblique; it is formed by the orbital surface of the greater wing of the sphenoid and the malar. Between it and the roof, near the apex, is the sphenoidal fissure, by means of which the third, fourth, ophthalmic division of the fifth and sixth nerves enter the orbit from the cranial cavity. The lower margin of the fissure presents near the middle a small tubercle, from which one head of the external rectus muscle arises. Between the outer wall and the floor, . near the apex, is the spheno-maxillary fissure, which allows the superior maxillary nerve to enter the infraorbital groove from the spheno-maxillary fossa. At the anterior margin of the fissure, the sphenoidal wing occasionally articulates with the maxilla, but frequently it is excluded by the malar. In front of the anterior extremity of this fissure is the orbital orifice of the malar canal. Near the outer extremity of the sphenoidal fissure a few small foramina may be seen, especially in old skulls, which allow branches of the middle meningeal artery to creep into the orbit. A vertical fissure, the spheno-malar, traverses the outer wall. It contains a very small foramen (the spheno-malar), which allows the temporal branch of the orbital nerve to escape from the orbit. This foramen is sometimes confined to the malar bone.

The inner wall, narrow and straight, is formed by the lachrymal, os planum of the ethmoid and a part of the body of the sphenoid. The ethmoid section of the transverse suture contains the orifices of the anterior and posterior ethmoidal

The Inner Wall of the Orbit.

canals: the former transmits the nasal nerve and anterior ethmoidal artery; the latter the posterior ethmoidal artery.

Anteriorly is the lachrymal groove and behind this the crest which gives origin to the tensor tarsi. This wall has three vertical sutures: one between the nasal process of the maxilla and the lachrymal, the ethmo-lachrymal and one between the os planum and body of the sphenoid. Occasionally the sphenoidal turbinal bone appears in the orbit between the os planum of the ethmoid and the body of the sphenoid.

The orbit communicates with the cranial cavity by the optic foramen and sphenoidal fissure; with the nasal fossa by means of the lachrymal duct; with the zygomatic and spheno- maxillary fossae by way of the spheno-maxillary fissure. In addition to these large openings, the orbit has six other foramina- the infra- orbital, malar, spheno-malar, anterior and posterior ethmoidal canals and the anterior dental canal opening into it or leading from it.

In old skulls the frontal sinuses occasionally extend into that portion of the horizontal plate of the frontal bone which forms the roof of the orbit.

The following muscles arise within the orbit: the four recti, the superior oblique and levator paljjebrcB superioris, near the apex; the inferior oblique on the floor of the orbit external to the lachrymal canal; and the tensor tarsi from the lachrymal crest. The margins of the spheno-maxillary fissm^e give attachment to the orbitalis muscle.

The nasal fossae or sinuses are two irregular cavities situated on each side of a median vertical septum, extending from the anterior part of the skull-base to the superior surface of the hard palate. They are somewhat oblong in section, but are narrower above than below.

Each fossa presents a roof, floor, inner and outer wall and opens in front by the anterior naris and communicates behind with the pharynx by the posterior naris.

The roof resembles that of a house with two sloping edges and an intermediate level portion. The anterior slope is formed by the posterior surface of the nasal bone and the nasal spine of the frontal. The horizontal portion corresponds to the cribriform plate of the ethmoid and the sphenoidal turbinal. The posterior

Section through the Nasal Fossa to show the Septum.

slope is formed by the inferior surface of the body of the sphenoid, an ala of th vomer and a small portion of the sphenoidal process of each palate bone.

The floor is wider than the roof, concave from side to side and has a sligh backward slope. It is formed mainly by the palatine process of the maxilla and completed posteriorly by the horizontal plate of the palate bone. Near it anterior part, close beside the septum, is the anterior palatine canal.

The septum, or inner wall, is formed by the crest of the sphenoid, the crest of the nasal bones, nasal spine of frontal, the mesethmoid, vomer and the median crest formed by the apposition of the palatine plates of the maxillae and the horizontal plates of the palate bones. The anterior border has a triangular outline,, limited above by the mesethmoid and below by the vomer. This receives the triangular cartilage of the nose. The posterior border is formed by the pharyngeal edge of the vomer. The septum is usually deflected to one side and is occasionally perforated. Sometimes a strip of cartilage, continuous with the triangular cartilage, persists between the vomer and mesethmoid.

The outer wall is formed by the nasal process and inner wall of the maxilla, the lachrymal, the ethmoidal and inferior turbinals, the vertical plate of the palate bone and the inner surface of the internal pterygoid plate. The outer wall presents three recesses or meatuses. The superior meatus is situated between the superior and middle turbinal; it opens posteriorly; three orifices are in relation with it, namely, the orifice of the posterior ethmoidal cells, the spheno-palatine foramen and the opening of the sphenoidal sinus. The middle meatus lies between the middle and inferior turbinals. It opens anteriorly and posteriorly. This meatus has two orifices communicating with it the opening of the antrum (which is of very irregular shape) and the termination of the infundibulum. The inferior meatus is situated between the inferior turbinal and the floor of the fossa; it presents near its anterior part, under cover of the turbinal, the terminal orifice of the nasal duct. This is the largest meatus, and, like the middle, opens anteriorly and posteriorly.

The anterior narial orifices are bounded above by the lower border of the nasal bones, laterally by the maxillae and inferiorly by the premaxillary portions of the maxillae. In the recent state they are separated by the triangular cartilage; in the dried skull the most anterior inferior limit is the anterior nasal spine.

Section through the Nasal Fossa to show the Outer Wall WITH THE Meatuses.

The posterior narial orifices are bounded above by the alae of the vomer, the sphenoidal process of the palate bones and the under surface of the sphenoid; externally by the internal pterygoid plates; and inferiorly by the posterior border of the horizontal plates of the palate bones. They are divided by the posterior border of the vomer and the posterior nasal spine.

The nasal fossae communicate with all the more important fossae and sinuses of the skull. By means of the foramina in the roof they are in connection with the cranial cavity. The infundibulum brings each fossa in communication with the frontal and anterior ethmoidal cells. The posterior ethmoidal and the sphenoidal cells open into the superior meatuses. The spheno-palatine foramina connect them with the spheno-maxillary fossae and an irregular orifice in each outer wall causes them to communicate with the antra. The nasal ducts connect them with the orbits and the anterior palatine canals with the buccal cavity.

The sutures visible in an anterior view of the skull are numerous and for the most part unimportant:

The transverse suture extends from one external angular process to the other.

The upper part of the suture is formed by the frontal bone; below are the malar, greater and lesser wing of the sphenoid, os planum, lachrymal, maxillary and nasal bones. A portion of this complex suture, lying between the sphenoid and frontal bones, appears in the anterior cranial fossa.

Other and less important fissures are the internasal, naso-maxillary, inter- maxillary and malo-maxillary. The small sutures visible in the orbit have been already mentioned in describing that cavity.

The Posterior Nares.

The following points are seen in an anterior view of the cranium: The glabella, a smooth space between the converging superciliary ridges. The ophryon is the most anterior point of the metopic suture. The nasion is the central point of the transverse suture.

The subnasal point is the middle of the inferior border of the anterior nasal aperture at the base of the nasal spine.

The alveolar point is the centre of the anterior margin of the upper alveolar arch.