THE CRANIUM. 15 
lage and membrane bones. Its superior and 
inferior margins meet posteriorly with the 
occipital segment ; laterally, they are separ- 
ated by the interposition of the squamosal, 
and the auditory bulla. 
i. The basi-sphenoid is a median flat tri- 
angular bone, the base of the triangle 
being posterior and lying immediately 
in front of the basi-occipital. Laterally, 
it is bounded by the pterygoids, ali- 
sphenoids, and squamosals. On the 
dorsal surface of the basi-sphenoid is 
a little hollow, the sella turcica, which 
lodges the pituitary body. 
ii. The ali-sphenoids arise from the sides 
of the basi-sphenoid as two wing-like 
bones, forming part of the floor of the 
cranial cavity. From the ventral sur- 
face of each ali-sphenoid, there projects 
a downwardly directed vertical plate 
of bone,the pterygoid process, whose 
anterior edge is connected with the 
palatine. Between the posterior por- 
tion of the ali-sphenoids, and the ex- 
occipital, the foramen lacerum me- 
dium passes; andthroughittheinternal 
carotid artery enters the cranial cavity. 
The basal portions of the ali-sphenoids 
are perforated by the foramen ovale, 
a large oval-shaped foramen transmit- 
