514 MAMMALIAN ANATOMY 



anterior cerebral part, has pushed the cranium over the face, which 

 thus appears to depend from its anterior end ; the assumption of the 

 upright posture has brought the foramen magnum almost in the centre 

 of the cranial base. 



None of these features are visible in the cat's skull. 



The student should now examine the base of the human skull in 

 detail. 



At the extreme anterior end is the arcuate alveolar border, with its 

 sixteen teeth ; it ends behind at the maxillary tuberosities. Behind 

 its middle point, in front, is the single anterior palatine fossa, from 

 which the mesopalatine suture is continued backward to the post- 

 nasal spine. The transverse palatine suture unites the palatine 

 processes of the maxillary and palatine bones. Near each outer pos- 

 terior corner is the posterior palatine foramen; just behind it are 

 several accessory palatine foramina. 



Posterior to these foramina is the hamular process of the inner 

 pterygoid plate; between this process and the flaring outer pterygoid 

 plate is the small pyramidal process of the palatine bone, forming 

 the lower part of the pterygoid fossa, which ends above where the 

 two plates come together. 



By tilting the skull slightly the student can look through the 

 posterior nares into the nasal chamber and examine the median par- 

 tition, the vomer, and the superior, middle, and inferior turbinated 

 bones, with the corresponding meatuses. On the roof of each nasal 

 fossa are the openings in the cribriform plate and the entrance to the 

 sphenoidal sinus ; on the outer wall are the spheno-palatine foramen, 

 the opening of the antrum, and the end of the lachrymal canal. 



Each posterior naris is bounded below by the palatine bones 

 (above in this position of the skull), medially by the vomer, laterally 

 by the inner pterygoid plate, and above by the under surface of the 

 body of the sphenoid, the vaginal process of the inner pterygoid plate, 

 the ala of the vomer, and part of the sphenoidal process of the 

 palatine bone. Between the vaginal process and the vomer is the 

 basipharyngeal canal; between the vaginal process and the sphe- 

 noidal process of the palatine is the pharyngeal or pterygo-palatine 

 canal for the pterygo-palatine nerves. On each side above the ptery- 

 goid fossa is a shallow scaphoid fossa for the tensor tympani muscle ; 

 it is pierced by inconstant foramina. 



