98 COMPARATIVE MORPHOLOGY OF VERTEBRATES. 
The chondrocranium of the MAMMALS has several peculiarities. There are 
four occipital vertebre, the last only with a complete vertebral character, all event- 
ually fusing with the synotic tectum. The dorsal part of the otic capsule chondrifies 
first, owing to the late development of the cochlear part of the ear in the lower half; 
and the capsules themselves have their axes inclined, so that the exit of the seventh 
nerve is on the anterior rather than on the lateral face. The trabeculz soon join 
the basal plate and from their sellar part an alary process is given off on either side 
EEE 
Fic. 102.—Chondrocranium of a pig, after Mead. as, alisphenoid; ¢l, posterior clinoid 
process; cr, fenestra cribrosa; end, foramen for endolymph duct: fm, foramen magnum; h, 
fossa hypophyseos; /sr, lateral superior recess: os, orbitosphenoid; I, parietal lamina; sm, 
septum nasi; é#, tectum nasi; 2-12, exits of nerves. - 
which extends upward to join an alisphenoid (ala temporalis) which chondrifies 
separately, but soon joins the otic capsule above, leaving between them the foramen 
ovale for the third branch of the fifth nerve, the other branches passing forward 
over the ala and then between it and the orbitosphenoid (ala orbitalis) through 
the sphenoidal fissure (foramen lacerum anterior). The ala orbitalis joins the 
trabecula by two processes, bar and processes sometimes forming a reduced inter- 
orbital septum. Later a marginal band (tenia marginalis) extends back from 
