134 



Anatomy of the. Rabbit. 



— p-pm. 



natural condition the cerebellum and related posterior portions of 

 the brain. If is partly set off from the middle cranial fossa by a 

 fold of the dura mater, the tentorium cerebelli, which projects 



inward from the dorsal and 

 lateral walls of the skull. 

 This fold is usually found 

 adhering to the internal sur- 

 face of the skull, unless the 

 latter has been very thor- 

 oughly cleared, and in all 

 cases its position is indicated 

 by a low ridge of bone. The . 

 marked difference in diameter 

 between the middle and pos- 

 terior cranial fossae is ac- 

 counted for by the great thick- 

 ness of the auditory portion 

 of the skull. The anterior 

 surface of the periotic bone 

 will be observed to form an 

 extensive posterior wall for 

 the middle cranial fossa. 



The floor of the middle 

 and posterior cranial fossae is 

 not smooth, like the external 

 base of the skull, but presents 

 in its anterior portion a pro- 

 minent elevation, the sella 

 turcica, which is borne on the 

 body of the posterior sphe- 

 noid. It contains a large 

 central depression, the hypo- 

 physeal fossa (fossa hypoph- 

 seos), which in the natural 

 condition lodges the hypo- 

 physis or pituitary body. The 

 aperture of the fossa is partly enclosed laterally by a pair of pointed 

 posterior clinoid processes (processus clinoidei posteriores), the 



..J.m. 



ZY 



-•OJ.a.e. 



p.j. 



f.m,o. 



Fig. 6i. Ventral surface of the skull : AS, alis- 

 phenoid (ala magna); B, basioccipital (basilar 

 portion of occipital); BS, basisphenoid (body of 

 posterior sphenoid) ; EXO.exoccipital; M, maxilla; 

 PL, palatine; PMX, premaxiUa; PR, presphenoid 

 (body of anterior sphenoid) ; SO, supraoccipital 

 (squamous portion of occipital); SQ, squamosal; 

 T, tympanic; 2Y, zygomatic. 



ch, choana; c.hy., hypoglossal canal; c.o., 

 occipital condyle; f.c.e., external carotid foramen; 

 f.in., incisive foramen; f.j., jugular foramen; f.l., 

 foramen lacerum; f.m., mandibular fossa; f.m.o., 

 foramen magnum; f.p.m., greater palatine foramen ; 

 f.s.a., anterior sphenoidal foramen; m.a.e., osseous 

 portion of external acoustic meatus; p.j., jugular 

 process; p.o.e., extern&l occipital protuberance; 

 p.pl., palatine process of maxilla; p.pm., palatine 

 process of premaxilla; p.pt., medial and lateral 

 laminae of pterygoid process of posterior sphenoid; 

 s.m,, spina masseterica. 



