SKELETON. 85 



reduced or even disappear, those remaining being connected by a one or two-jointed 

 copula. 



The chondrocranium of the larval AXURA (Rana, fig. 86) differs considerably 

 from that of other amphibia as well as from the adult conditions. Like all amphib- 

 ians it is platybasic. The pterygoquadrate has, besides the normal otic and 

 epipterygoid processes, a cranio-quadrate process connected with the nasal region, 

 in front of which is the articulation of the lower jaw. In front of the cornua are a 

 pair of suprarostral cartilages and a similar pair of infrarostrals lie in front of the 



FIG. 86. Chondrocranium of tadpole of Rana before the metamorphosis; after Gaupp. 

 c.,ant, anterior canal; els, superior labial cartilage; ctr, cornu trabeculse; car, foramen for 

 carotid; eoct. c, external canal; /e, ethmoid fenestra; m, MeckeFs cartilage; pc, posterior 

 canal; po, otic process of quadrate; pr. as.' ascending process of quadrate; q, quad- 

 rate; tm, tectum medialis; ttm, taenia tecti marginalis; tsyn, tectum synoticum; I-V, nerves 

 and nerve exits. 



Meckelian, from which they are apparently derived. These four rostrals form a 

 ring around the suctorial mouth and recall the labial cartilages of the elasmobranchs 

 and the annular cartilage of the cyclostome mouth. 



At the time of metamorphosis the changes are great, and as the result is more 

 like the chondrocranium of other amphibia, the larval condition must be regarded 

 as adaptive rather than ancestral. The suprarostrals disappear and the jaw 

 shifts the hinge back to the normal position, this being accompanied by the elon- 

 gation of MeckePs cartilage, an absorption of the ascending process and a folding 

 of the pterygoquadrate bar. At the same time a pterygoid grows out in front to 

 join an antorbital process from the cranium. A stapes develops and connects 



