706 APLTS. VO Ie 
its posterior portion is marked off from the rest of the bone by 
a groove, sometimes faint and sometimes well defined, which 
runs across the ventral surface of the bone and then upward 
and forward along its sides, but not across its dorsal surface. 
In front of this groove, on the ventro-lateral surfaces of the 
bone, there are two large, oblong, flattened surfaces, one on 
either side of the middle line. They are inclined at an angle 
to each other, raised somewhat above the level of the rest of 
the bone, and extend to its anterior end. On them the 
hind ends of the parasphenoid rest, and the development of 
this part of the skull shows that these flattened elevations, in 
their posterior portion at least, must be, like portions of the 
vertebrae, of membranous, and not of cartilaginous, origin. 
Above the dorso-lateral edges of the two surfaces, and in front 
of the posterior, solid end of the bone, the basioccipital becomes 
thin, and its thin upper edges diverge from behind forward. 
Between the two surfaces, on the ventral surface of the bone, 
there is a median, depressed portion, or groove, and at the 
anterior end of this groove, in the middle line of the head and 
extending directly forward, there is a long, flat, thin process, 
which, viewed from beneath, has the appearance of a thin 
wedge or blade of bone driven into the basioccipital from 
its ventral surface, and slightly separating the bone into two 
halves. The anterior end of this process almcst reaches the 
posterior end of the hypophysial fenestra. 
Between the hind ends of the two flattened and slightly 
elevated ventro-lateral surfaces of the basioccipital, and hence 
between the hind ends of the parasphenoid, are the two little 
openings (caz) described by Sagemehl (No. 104, p. 195), one 
on each side of the middle line of the head. From each of 
them arise one or two canals which run outward, upward, and 
forward, and have their dorsal opening, or openings, at about 
the middle of the lateral surface of the basioccipital, dorsal to 
the flattened, ventro-lateral surface of that bone, and hence 
dorsal to the lateral edge of the parasphenoid. The anterior 
of the two canals, where there are two, is the smaller, and 
through it a small sympathetic nerve passes; through the 
posterior and larger canal a spinal artery passes, This artery 

