84 



VERTEBRATE SKELETON 



ethmoid and basal plates and closing the sella turcica in the middle 

 line. 



The visceral arches are continuous bars at first (hg. 86), separating 

 later into the parts (Fig. 71) of the adult, and still later becoming 

 connected by copulae in the mid-ventral line. The halves of the 

 pterygoquadrate also fuse in front. The labials are late in appear- 

 ing and branchial rays arise independently of the arches. 



Fig. 88. — Ventral side of skull of skate (Gegenbaur, '72). cp, copula; h, hyoid; hm, 

 hyomandibular; tnk, Meckelian; nc, nasal capsule; /j?, pterygoquadrate; r, rostrum. 



The adult has lost the characteristic flexure of the young, only 

 traces of it remaining in the sharp angle of the dorsum sellae and the 

 marked basal angle on the ventral surface (fig. 87). The floor is 

 complete, as is the roof as far forwards as the level of the nasal 

 capsules, in front of which cartilage is replaced by membrane, easily 

 torn away, leaving the large anterior fontanelle which extends to the 



