COMPARATIVE ANATOMY 23 



vertebrates: the basisphenoid and the paired pterygoids and 

 alisphenoids. 



In the adult cat the basisphenoid is on the ventral surface 

 of the skull between presphenoid and occipital. It is shield 

 shaped with the apex pointing forward. Its dorsal surface has a 

 projection, the dorsum sellae. Immediately interior to this 

 projection is a deep excavation, the sella turcia (meaning Turkish 

 saddle), in which is lodged the pituitary gland. 



The wings are thin plates attached by their median borders 

 to the lateral surfaces of the basisphenoid. Each wing is com- 

 posed of a pterygoid process, which extends forward on the roof 

 of the mouth between the presphenoid and the palatine; and 

 an alisphenoid process, which extends forward and dorsally, 

 meeting presphenoid, frontal, parietal, and temporal. 



15. Ethmoid. — This is an unpaired much-coiled bone, 

 partially visible on looking into the nares. Examination of a 

 separate bone will show that it consists of several parts. 



a. The cribriform plate (cribrum, sieve), is so called because 

 of its many perforations for the passage of the olfactory nerves. 

 It forms the dividing wall between brain cavity and nasal 

 cavity. 



b. The lamina perpendicularis (lamina, a thin sheet), 

 extends anteriorly from the center of the cribriform plate and 

 forms part of the septum between the nostrils. 



c. The ethmoturbinates, a complicated mass of thin folded 

 sheets of bone, nearly fill the nasal cavity. The turbinates are 

 attached to the vomer, the nasal, and the maxillary bones. 



16. Mandible {inferior maxillary). — This forms the lower 

 jaw. It is made up of two halves immovably united at the 

 median symphysis. Each side bears three incisor teeth, one 

 canine, two premolars, and one molar. Between canine and 

 premolars is a diastema (an open space between teeth). 



On the posterior part of the median surface of each ramus 

 of the mandible Is the inferior dental foramen, carrying nerves 

 and arteries which emerge again through the two mental foramina 

 on the external surface just below the diastema. 



Posteriorly the mandible is marked by six prominent features : 

 a. The coronoid fossa, a large fossa on the lateral surface 

 for the Insertion of the masseter muscle. 



