134 0 
ANATOMY OF THE RABBIT. 
natural condition the cerebellum and related posterior portions of 
the brain. 
It is partly set off from the middle cranial fossa by a 
fold of the dura mater, the tentorium cerebelli, which projects 

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, premaxilla; PR, presphenoid 
(body of anterior sphenoid); SO, supraoccipital 
(squamous portion of occipital); SCG, squamosal; 
T, tympanic; ZY, zygomatic. ; 
ch, choana; c.hy., hypoglossal canal; CHOKS 
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., external 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. 
Fic. 61. 
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 
