THE CAT 269 



perforates this bone on each side. In front of the presphenoid are 

 the paired palatine bones, which form the hard palate. In the base 

 of the zygomatic process of the temporal bone is the glenoid cavity, 

 in which the lower jaw articulates. 



In addition to the foramina already mentioned the large foramen 

 jugale and the hypoglossal foramen will be seen. The former 

 foramen is a large hole, between the tympanic bulla and the occip- 

 ital bone, through which the glossopharyngeal, vagus, and spinal 

 accessory nerves pass ; the latter foramen is in the hinder margin 

 of the former. 



Exercise 59, Draw a view of the ventral aspect. 



With a fine saw divide the skull into two slightly unequal halves 

 by a longitudinal dorsoventral incision just at one side of the 

 median line, and study its inner surface. The interior of the skull 

 is divided into three cavities,— the cranial, the auditory, and the 

 nasal cavity, which contain the brain, the auditory, and the olfac- 

 tory organs respectively. 



The cranial cavity, in turn, is divided into the cerebellar, cere- 

 bral, and olfactory fossae. The first of these occupies the hinder 

 part of the skull, being bounded anteriorly by the tentorium, the 

 transverse partition extending inward from the parietal bones. In 

 the floor of this cavity is the internal auditory meatus, a large 

 depression divided by a partition into two parts, the dorsal part 

 containing the foramen of the facial nerve, and the ventral part 

 containing a number of small foramina of the auditory nerve. 

 Beneath this meatus is the hypoglossal foramen, posterior to which 

 is the condyloid canal, through which a vein passes. 



The cerebral fossa is the largest of the three fossae ; it occupies 

 the entire central portion of the cranial cavity. In its floor is the 

 large optic foramen, just back of which is a large circular depres- 

 sion, the sella turcica, in which the hypophysis lies. 



The olfactory fossa occupies the anterior end of the cranial 

 cavity and lies beneath the frontal bones. Its anterior end is 

 bounded by the ethmoid bone, in which the mesethmoid portion, 

 the labyrinths, and the cribriform plate may be distinguished. 

 The mesethmoid, the median portion, is a vertical plate which sep- 



