58 THE SKELETON OF THE CAT. 
the cerebral fossa (//) in the middle, for the cerebrum; the 
small olfactory fossa (///) at the cranial end for the olfactory 
bulb of the brain. 
The cerebellar fossa (/) is bounded caudally by the occipital 
bone enclosing the foramen magnum (Fig. 42, 2). Its ventral 
surface is formed by the basilar portion of the occipital and the 
petrous portions of the temporals; its lateral surface by the 
mastoid portions of the temporals and parts of the parietals and 
occipital. Its roof is formed by the parietals and interparietal. 
Craniad the cerebellar fossa is partly separated from the cere- 
bral fossa by the tentorium (Fig. 42, ¢; Fig. 43, /) formed by 
the two parietals: this encloses a quadrangular opening by 
which the two fosse communicate. The caudal, dorsal, and 
lateral walls of the cerebellar fossa are deeply marked by fosse 
for the lobes of the cerebellum; the small appendicular fossa 
.(Fig. 43, ¢), forming a deep indentation in the petrous bone 
near its dorsocaudal end, is particularly noticeable. 
The following openings are found in the walls of the cere- 
bellar fossa. Caudad is the large foramen magnum (Fig. 42, a) 
by which the brain-cavity communicates with the vertebral 
canal. Near the caudal margin of the foramen magnum, on 
its lateral side, just mediad of the dorsal end of the occipital 
condyle, is the caudal opening of the condyloid canal (Fig. 43, 2) 
which passes craniad through the substance of the occipital 
bone to open just caudad of the petrous: it transmits a vein. 
The condyloid canal varies greatly in size in different speci- 
mens. A few millimeters craniad of the edge of the foramen 
magnum on the floor of the fossa is the small opening of the 
hypoglossal canal (Figs. 42 and 43, 4), for the twelfth nerve. 
Just craniad of this, at the caudomedial border of the petrous, 
is the large jugular foramen (c). On the petrous itself, near 
the middle, is the internal auditory meatus (@) divided into the 
dorsal facial canal for the seventh nerve, and a ventral passage 
for the eighth nerve. At the cranial end of the cerebellar 
fossa is the large opening bounded by the free edges of the 
tentorium. . 
The cerebral fossa forms much the largest part of the 
cranial cavity, It is bounded by the parietals (Fig. 43, 3°), 
