Part 35

Sq.o., Supraoccipital; E.o., exoccipital; B.o., basioccipital; B.s., body of sphenoid; Sq., squamous temporal bone; V, vomer; Mx., maxilla; Pa., horizontal part of palate bone; P.p., palate process of maxilla; Z, malar bone; J, premaxilla; D.c., canine tooth; J1–3, incisor teeth; O, temporal fossa; 1, occipital crest; 2, for. magnum; 3, occipital condyle; 4, paramastoid (styloid) process; 5, bulla ossea; 6, for. lacerum basis cranii; 7, pterygoid process of sphenoid; 8, posterior nares; 9, anterior palatine foramen; 10, palatine cleft. (Struska, Anat. d. Haustiere.) ]

The =sphenoid bone= is short and resembles that of the ox in general. The body is narrow. The pituitary fossa is very deep, and is limited behind by a prominent dorsum sellæ; the dorsum bears lateral projections, the =posterior clinoid processes=. The foramen ovale is absent, being included in the foramen lacerum anterius. The other foramina are like those of the ox. The pterygoid process is broad and twisted. Its base is not perforated and its free edge is thin and sharp. It concurs with the pterygoid and palate bones in the formation of the pterygoid fossa, which opens backward and is not present in the horse or ox. The sphenoidal sinus is very large and occupies the body, the temporal wings, and a great part of the pterygoid processes in the adult; it is continued into the temporal bone as mentioned above.

The =ethmoid bone= has a relatively long perpendicular plate, which is marked by ridges corresponding to the ethmoidal meatuses. The cribriform plate is extensive and very oblique, so that it and the crista galli are almost in line with the basi-cranial axis. A linear series of relatively large foramina is found on either side of the crista. The lateral mass consists of five endoturbinals and eighteen ectoturbinals (Paulli). The lamina papyracea concurs in the formation of the pterygo-palatine fossa.

FACE

The =maxilla= is extensive. Its external surface forms a longitudinal groove, which is continued upon the premaxilla in front and the facial parts of the lacrimal and malar behind. The infraorbital foramen—sometimes double—is large and is situated above the third or fourth cheek tooth. The alveolus for the canine tooth produces a ridge at the anterior end which is very pronounced in the boar. The facial crest extends forward from the root of the zygomatic process and fades out behind the infraorbital foramen; in some specimens it is prominent and thin-edged, in others it is rounded and projects little. The zygomatic process is short but stout and buttress-like; it is overlapped externally by the malar. The maxillary tuberosity forms in the young subject a long bulla, which occupies most of the pterygo-palatine fossa and contains the developing permanent molars; after the eruption of the teeth the tuberosity flattens and joins the vertical part of the palate bone. The palatine process is very long and is marked in its anterior part by transverse ridges corresponding with those of the mucous membrane of the palate. The anterior palatine foramen is near the junction with the palate bone; from it the palatine groove can be traced distinctly along the entire length of the process. The alveolar border presents a large alveolus for the canine tooth at its anterior end; behind this are seven alveoli for the cheek teeth, which increase in size from first to last. The maxillary foramen and infraorbital canal are very large. The maxillary sinus is small.

The body of the =premaxilla= is narrow and prismatic. It presents three alveoli for the incisor teeth, which are separated by short intervals and diminish in size from before backward. As in the ox, a narrow space separates the right and left bones and takes the place of the foramen incisivum. The palatine process is long and narrow. The nasal process is very extensive and is somewhat rhomboid in outline. Its upper border forms a very long suture with the nasal bone, and the lower articulates to about the same extent with the maxilla. The palatine fissure is relatively wide.

The horizontal part of the =palate bone= forms a fourth to a fifth of the length of the palate; its palatine surface is triangular, the apex being anterior; its nasal surface is deeply grooved and smooth. A pterygoid process (processus pyramidalis of man) projects backward and downward, and its thick rounded end is received between the pterygoid process of the sphenoid and the pterygoid bone. The perpendicular part is largely overlapped externally by the maxilla and concurs in forming part of the palatine canal. Superiorly the two plates separate and inclose an air-cavity which opens into an ethmoidal meatus. The inner plate curves inward and unites with the vomer and ethmoid to form a horizontal plate (Lamina transversalis), which divides the posterior part of the nasal cavity into an upper olfactory part and a lower respiratory part.

The =pterygoid bone= is nearly vertical in direction, and is narrow in its middle, wide at each end. The external surface is free below and forms the inner wall of the pterygoid fossa. The lower end is notched and forms a distinct hamulus.

The =nasal bone= is very long and its width is almost uniform, except at the anterior end, which is pointed and reaches almost as far forward as the premaxilla. The facial surface is flattened from side to side. In profile it is nearly straight in some subjects, variably concave in others. The external border is free to a small extent in front only; otherwise it is firmly connected with the premaxilla and maxilla. In the adult the frontal sinus extends into the posterior part of the bone.

The =lacrimal bone= is very sharply bent. Its facial surface presents a deep depression, surmounted by a ridge or tubercle. On or close to the orbital margin are two lacrimal foramina which lead to the lacrimal canals. The orbital surface presents a fossa in which the inferior oblique muscle of the eyeball arises, and its lower part bears a crest, which is crossed obliquely by a vascular furrow. The upper border articulates with the frontal only. The bone concurs in the formation of the maxillary sinus.

The =malar bone= is strongly compressed from side to side. Its facial surface is small and presents a fossa which is continuous with the depressions of the maxilla and lacrimal. The orbital surface is still smaller and is smooth and deeply grooved. The zygomatic process is very extensive, especially in the vertical direction. Its external surface is convex and free, and bears a rough eminence in its middle. Its internal surface is concave; it is overlapped in front by the maxilla, and in the remainder of its extent is free and smooth. The upper border is thick and rounded in front, where it forms the lower part of the orbital margin; behind this it forms an extensive notch which receives the zygomatic process of the temporal. (It might be regarded as dividing into frontal and temporal branches.) The lower border is convex and becomes thinner behind.

The =turbinal bones= resemble those of the ox. The superior turbinal is, however, relatively longer, less fragile, and more firmly attached to the nasal bone. There is no middle turbinal.

The =vomer= is very long. The anterior extremity reaches to the body of the premaxilla or very close to it. The lower border is received into a groove formed by the nasal crest of the maxillæ and palate bones and in front by the palatine processes of the premaxillæ. The posterior border is concave, thin, and sharp.

The =os rostri= (or prenasal bone) is situated in the snout between the nostrils. It has the form of a short three-sided prism. The upper surface is convex and is notched at each end. The lateral surfaces are concave, smooth, and converge below, forming a grooved lower border. The posterior surface is triangular, notched centrally, and rough laterally. The anterior surface is deeply pitted and is surrounded by an irregular sharp border.

The =mandible= is very strong, and differs very much from that of the horse or ox. The body narrows decidedly in front; the lingual surface is deeply concave; the mental surface is strongly convex, slopes downward and backward, and forms a distinct prominence at the point of divergence of the rami. Above this prominence is a pair of foramina. The alveolar border presents six alveoli for the incisor teeth, and a little further back two large cavities for the canine teeth. There are two pairs of mental foramina of considerable size and a variable number of smaller ones. The rami diverge more than in the horse or ox, and the upper part is somewhat incurved. The horizontal part is very thick and strong. Its outer surface is strongly convex from above downward. The inner surface is prominent over the roots of the molar teeth and overhangs the concave lower part. The alveolar border is thin in front and widens behind; it does not follow the axis of the ramus, but runs nearly straight and produces the marked overhang noted above. There are seven alveoli for the lower cheek teeth, which increase in size from before backward. The first is small, not always present in the adult, and is separated by short spaces from the second and the canine alveolus. The vertical part is relatively wide above. The condyle is convex in both directions, wide in front, narrow and declivitous behind. The very small and thin-edged coronoid process is not quite so high as the condyle, from which it is separated by a very wide notch. The mandibular foramen is large. The two halves of the bone unite soon after birth in the improved breeds.

The body of the =hyoid bone= is broad from before backward, short transversely, and bears on its ventral aspect a very short pointed lingual process. The thyroid cornua are wide and curved, concave and grooved dorsally; their ends are attached to the thyroid cartilage of the larynx by rather long bars of cartilage. The small cornua are short, wide, and flattened dorso-ventrally; they are attached to short bars which project from the junction of the body and thyroid cornua. The middle cornu is a little longer than the small cornu, but is relatively slender; it is largely cartilaginous in the young subject and does not ossify at either end. The great cornu is a very slender rod, slightly enlarged at either end; the upper extremity is attached to the hyoid process of the temporal by a rather long and wide bar of cartilage.

FIG. 112.—MANDIBLE OF PIG.

a, Body of mandible; b, horizontal part of ramus; f, vertical part of ramus; c, interalveolar border; c′, interval between canine and corner incisor; c″, interval between first and second premolars; d, mental foramina; e, vascular impression; g, coronoid process; h, condyle; i, sigmoid notch; k, mandibular foramen; 1–7, cheek teeth, 8, canine tooth; 9, 10, 11, incisors. (Ellenberger-Baum, Anat d. Haustiere.) ]

THE SKULL AS A WHOLE

The =length= and the =profile= contour vary greatly in different subjects. Primitively the skull is long—especially in its facial part—and the frontal profile is almost straight. The condition is very pronounced in wild or semi-feral pigs, and exists also in the improved breeds during extreme youth. Most of the latter are decidedly brachycephalic when fully developed; the face is “dished” in a pronounced fashion. The frontal region slopes sharply upward, and the nasal region is shortened, and in some specimens even distinctly concave in profile. The supraorbital foramina are about midway between the orbital margin and the frontal suture. The supraorbital grooves extend forward from the foramina to the nasal region and turn outward and downward toward the infraorbital foramina over the ridges which separate the nasal and lateral regions.

The =lateral surface= is triangular when the mandible is included. The temporal fossa is entirely lateral and its long axis is almost vertical. It is bounded above by the occipital crest, behind by the temporal crest, in front by the parietal crest, and is marked off from the orbital cavity by the supraorbital process and a curved crest which extends from it to the root of the pterygoid process. The zygomatic arch is strong, high, and flattened from side to side. Its root is notched above and bears a projection below. It curves sharply upward behind and forms a pointed recurved projection above and in front of the external auditory meatus. The orbit is small. Its margin is deficient behind in the dry skull, thick and rounded in front and below. The cavity is limited below by a ridge on the frontal and lacrimal bones, and is separated by a crest from the temporal fossa. The inner wall is perforated above by the orbital opening of the supraorbital canal, and below by the optic and ethmoidal foramina; on its antero-inferior part is the fossa in which the inferior oblique muscle of the eye takes origin. Two lacrimal foramina are found on or close to the anterior margin. The pterygo-palatine fossa is well defined; its upper part forms a deep groove which leads from the large foramen in the sphenoid (like that of the ox) to the very large maxillary foramen. The preorbital region is deeply grooved in its length and is clearly marked off by a ridge from the nasal and frontal regions. The facial crest is short, usually thin-edged, and lies above the fifth and sixth cheek teeth. A little (ca. 2 cm.) in front of it is the infraorbital foramen. There is a ridged prominence over the canine alveolus. In some skulls the anterior part of the upper jaw is inclined upward.

The most striking features of the =basal surface= are as follows: The paramastoid processes are extremely long, less flattened than in the horse and ox, and nearly vertical. At the inner side of the root of each is the hypoglossal foramen, and in front of it are the stylo-mastoid foramen and a deep cavity in which the hyoid process is concealed. The bulla ossea is long, compressed laterally, and bears a sharp, short, muscular process. The basioccipital is wide and flattened; it bears a median crest and two lateral tubercles. The posterior nares are small and are wider below than above. On either side of them is the tuberosity of the palate bone, and above this is the pterygoid fossa. The palate is remarkably long and is relatively narrow. It constitutes about two-thirds of the entire length of the skull. It is widest between the canines and premolars and narrow at each end. It is marked by a crest medially and by the palatine foramen and groove laterally. The anterior part bears transverse ridges. It is moderately arched from side to side. In some specimens it is nearly straight or slightly concave in its length; in others it curves upward to a variable degree in front. The posterior end always slopes upward more or less.

The =posterior= or =nuchal surface= is remarkable for its height and the breadth of the occipital crest. The central part above the foramen magnum is smooth and concave from side to side, and is bounded laterally by ridges, which converge below and end on two tubercles at the upper margin of the foramen magnum. The surface is separated from the temporal fossæ by the temporal crests, which curve downward and outward and blend with the external auditory canals. The mastoid process has the form of a plate which overlaps the root of the paramastoid process and bears a crest on its anterior part.

The =cranial cavity= is small, in spite of the great size of the cranium; the discrepancy is due to the enormous development of the frontal sinuses in the adult. It is relatively longer, but much lower than that of the ox. Its width is greatly diminished between the orbits. The olfactory fossæ are extensive and very oblique. The floor resembles that of the ox, but the foramen ovale is absent, the dorsum sellæ is more developed, and the foramen lacerum basis cranii is like that of the horse. Two oblique lateral crests clearly mark the limit between the cerebral and cerebellar compartments. The tentorium osseum and the parieto-temporal canals are absent.

The =nasal cavity= is very long. Its posterior part is divided by a horizontal plate into olfactory and respiratory parts. The olfactory part or fundus is above, and contains the ethmoturbinals and ethmoidal meatuses. The lower part is continuous with the inferior meatus and leads to the pharyngeal orifice; hence it is sometimes called the naso-pharyngeal meatus. The bony roof is almost complete in front on account of the great length of the nasal bones.

The =frontal sinus= is a vast excavation in the adult animal. It involves all of the roof and almost all of the sides of the cranium, and extends forward into the roof of the nasal cavity a variable distance—sometimes as far as a transverse plane through the infraorbital foramina. The septum between the right and left sinuses is usually deflected in an irregular manner in its middle part, but is practically median at either end. Each sinus is subdivided by numerous septa, some of which are complete. Thus the sinus is divided into compartments, each of which communicates with an ethmoidal meatus.

In the young pig the sinus is small and is confined to the anterior part of the frontal bone. Later it extends backward, outward, and to a less extent forward. In the old subject it penetrates laterally into the supraorbital process and the root of the zygomatic process of the temporal bone, and behind almost down to the foramen magnum and the occipital condyles. It then consists of six to eight compartments usually.

The =maxillary sinus= is relatively small. Its anterior end is a little less than an inch (ca. 2 cm.) behind the infraorbital foramen, and it extends upward into the lacrimal and backward into the malar bone. The infraorbital canal passes along its floor, and the roots of the molar teeth do not project up into it. It does not communicate with the frontal and sphenoidal sinuses, but with the posterior part of the middle meatus by means of a considerable orifice.