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, a). 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, e\ Fig. 43, /) formed by 

 the two parietals: this encloses a quadrangular opening by 

 which the two fossae communicate. The caudal, dorsal, and 

 lateral walls of the cerebellar fossa are deeply mark'cd by fossae 

 for the lobes of the cerebellum; the small appendicular fossa 

 (Fig. 43, r), 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, a) 

 which passes craniad through the substance of the occipital 

 bene 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, l>), 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'), 



