12 ANATOMY OP THE RAT 



petrosal and occipital bones. This foramen transmits the 

 ninth (glossopharyngeal), tenth (vagus), and eleventh 

 (accessory) cranial nerves. The carotid foramen is an- 

 terior to the jugular foramen, between the tympanic bulla 

 and the basioccipital bone. Near the posterior ends of the 

 pterygoid processes is a pair of foramina which communi- 

 cate with one another by a horizontal space in the basi- 

 sphenoid bone. A large oval foramen lies immediately 

 anterior to the one just mentioned. Note the communica- 

 tion of this oval foramen with the superior orbital fissure. 

 'Ventral to the foramen ovale another large oval foramen 

 perforates the posterior part of the lateral pterygoid proc- 

 ess. Note the two slits in the cranium, dorsal and posterior 

 to the choana, communicating with the anterior lacerated 

 foramen. 



The prepalatine foramina are two conspicuous slits on 

 the roof of the mouth in the region of the diastema. They 

 are surrounded by the maxillary and premaxillary bones. 

 The postpalaMne foramina perforate the roof of the mouth 

 near the lateral margin of each palatine bone. A bristle 

 inserted through the foramen will show its communication 

 with the groove on the floor of the orbito-temporal fossa. 



Exercise III. Draw and label the ventral view of the cranium. 



Interior of the cranium. Bisect the skull vertically in 

 a plane slightly at one side of the sagittal plane. Use a 

 sharp bone saw with small teeth. Care should be exercised 

 to injure the bones as little as possible. 



Two cavities will be observed, the cranial cavity for the 

 brain, and the nasal cavity. The cranial cavity is sub- 

 divided further into the cerebellar, cerebral, and olfactory 

 fossae. 



The cerebellar fossa holds the cerebellum. It occupies 

 the posterior part of the cranium and is partially sepa- 



