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.
The =sphenoidal sinus= is very large. It involves the body, pterygoid
processes, and temporal wings of the sphenoid bone, and extends into the
squamous temporal. It communicates with the ventral ethmoidal meatus.
There is a small sinus in the perpendicular part of the palate bone
which communicates with an ethmoidal meatus.