THE CHONDROCRANIUM IN THE ICHTHYOPSIDA. 95 



the occipital arch is in essentially the same condition that 

 it was in the third stage. So also are the parachordals, 

 except that the union with the capsular floor is now com- 

 plete upon both sides. 



The otic capsules present several new features. From 

 their point of fusion with the occipital processes marginal 

 expansions (Figs. 9 and 11, loc) extend medially over the 

 sides of the cranial cavity. Passing forwards they approach 

 each other and unite to form the synotic tectum {st) 

 which terminates anteriorly in a short median process 

 {tm) the "tjeniatecti medialis" of Gaupp. In the me- 

 dian wall of the capsule there are now four small aper- 

 tures, of which three (Fig. 11) lie in a horizontal row 

 near the floor of the cranium, while the fourth is more 

 dorsal in position. Passing from in front backwards, the 

 first foramen of the row is the one traversed by the 

 seventh and one l)ranch of the eighth nerve {yii-\-viii). 

 The second branch of the eighth passes through the sec- 

 ond foramen (vui), and the third aperture of the row is 

 traversed by the perilymphatic duct (pf) . The fourth 

 aperture, higher up in the wall above the foramen for the 

 second branch of the eighth nerve, is the foramen for the 

 endolymphatic duct (ef). 



At the anterior end of the otic capsule there are three 

 new connecting cartilages joining it with the trabecula on 

 the one hand, and on the other with the quadrate. The 

 process joining the postero-dorsal point of the trabecular 

 crest with the opposite wall of the capsule is relatively 

 slender ; w^hile the other two processes, the otic (op) 

 and palato-basal (j^^), iu*e formed by the fusion of u greater 

 part of the dorso-median surface of the body and otic 

 process of the quadrate with the adjacent wall of the cap- 

 sule and the margin of the basilar i)hite. A blood vessel, 

 which passes dorso-ventrally around the anterior end of 



