THE SKELETAL SYSTEM 13 



rated from the cerebral fossa by an incompletely ossified 

 lateral partition, the tentormm. The ossified portion of 

 the tentorium is/ a dorsal extension of the petrosal bone, 

 which forms a part of the lateral wall of the cerebellar 

 fossa. The floccular fossa is a relatively large cavity occu- 

 pying the poster odorsal region of the petrosal bone. Its 

 opening into the cranial cavity is an oval aperture con- 

 siderably narrower than the cavity itself. The cerebral 

 fossa is the largest division of the cranial cavity. It in- 

 closes the cerebrum. The foramina observed in the study 

 of the lateral view may be identified easily by thrusting 

 a bristle through each foramen from the outside. The 

 olfactory fossa is a laterally compressed cavity opening 

 behind into the cerebral fossa and bounded in front by the 

 cribriform plate. This cavity contains the olfactory lobes 

 of the brain. The branches of the olfactory nerve enter 

 the nasal cavity through the numerous foramina in the 

 cribriform plate. In a cranium from which the roof has 

 been removed, the cribriform plate will be seen to be heart- 

 shaped. 



Though the nasal cavity can be satisfactorily studied 

 in a longitudinal section of the skull, it can be seen to the 

 best advantage if the dorsal and lateral bony wall of the 

 cavity be removed. In doing this care should be taken to 

 preserve intact the nasal bones and their delicate ventral 

 processes, and while chipping away the lateral wall to 

 injure as little as possible the delicate turbinal bones at 

 the back and sides of the nasal cavity. The nasal cavity 

 is tubular in form posteriorly {naso-pharyngeal duct), and 

 terminates at the single posterior naris, or choana. Its 

 external opening is through the two anterior nares at the 

 anterior end of the snout. The nasal cavity is bounded 

 dorsally by the nasal bones, posteriorly by the cribriform 

 plate and maxillary bones, ventrally by the premaxillary, 



