THE DOG’S SKULL. 
fossa, and converges in a fan-like 
manner to its point of insertion into 
the coronoid process of the mandible. 
ec. The frontal segment forms the anterior 
boundary of the brain case; it lies anterior 
to the parietal segment, with which it articu- 
lates. 
i. The pre-sphenoid is a median bone in 
front of the basi-sphenoid, bounded 
laterally by the pterygoids, and the 
posterior portion of the palatines. Its 
ventral or basal portion is straight, 
with a somewhat irregular dorsal por- 
tion. It is cancellous or spongy in 
texture. Its posterior and dorsal por- 
tion forms the lower margin of the 
optic foramina, through which the 
optic nerves pass out; anterior to this 
it diverges on either side of the median 
line,and forms part of the inner walls 
of the orbits. 
ii. The orbito-sphenoids are a pair of 
bones, forming part of the wall of the 
orbits and cranium. They are fused 
with the pre-sphenoid, and united su- 
turally with the frontals, ali-sphenoids, 
and squamosals. Their posterior bor- 
ders form the upper marein -or the 
optic foramina. 
iii. The frontals are a pair of membrane 
