THE SKULL AS A WHOLE 175 



above this is the pterygoid fossa. The palate constitutes about two-thirds of the 

 entire length of the skull, and is relatively narrow. 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 m front. The posterior end always slopes upward more or less. 



The nuchal surface is remarkable for its height and the breadth of the nuchal 

 crest. The central part above the foramen magnum is smooth and concave from 

 side to side, and is bounded laterally by ridges, which converge ventrally and end 

 on two tubercles at the upper margin of the foramen magnum. The surface is 

 separated from the temporal fossse bj- the temporal crests, which curve downward 

 and outward and blend with the external acoustic meatus. 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 craiiial 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 fossse are extensive and very ob- 

 lique. The floor resembles that of the ox, but the foramen ovale is absent, the 

 dorsum sella is more developed, and the foramen lacerum is like that of the horse. 

 Two oblique lateral crests clearly mark the limit between the cerebral and cerebellar 

 compartments. The internal occipital protuberance and the temporal canal are 

 absent. 



The nasal cavity is verj^ long. Its posterior part is divided by the lamina 

 transversalis into olfactory and respiratory parts. The olfactory part or fundus is 

 dorsal, and contains the ethmoturbinates and ethmoidal meatuses. The ventral 

 part is continuous with the ventral meatus and leads to the pharyngeal orifice; 

 hence it is 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 com- 

 municates 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 nasi 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 palatine bone which 

 communicates with an ethmoidal meatus. 



