SKULL — AMPHIBIA 



125 



membrane bones. The pterygoid process grows from the anterior side of the 

 quadrate, but, with the exceptions noted on p. 121, it ends freely in front. The 

 Meckelian cartilages of the two sides are separate in front at first, but are 

 continuous cartilage later. At most there are four branchial arches, the posterior 

 two being more rudimentary or even absent. Each arch has not more than two 

 parts, usually called cerato- and hypobranchial (sometimes regarded as epi- 

 and ceratobranchial). Not infrequently the upper ends of the ceratobranchials 

 of the several arches are fused. The copular series often continues behind the 

 attachment of the arches. The arches themselves undergo considerable changes 

 at metamorphosis, the Perennibranchs being the most conservative in this 

 respect. 



Fig. 132. — Hybranchial skeletons of Urodeles. .4, B. Triton cristatiis (Stohr, '77); 

 A, embryo 7 mm. long; B, 10 mm. C, D, Triton tceniatus (Gaupp, '05); C, larva 20 

 mm.; D, after metamorphosis; E, adult Amblystoma punctatum; F, adult Proteus 

 (Wiedersheim, '77). Cartilage stippled, bones black. 



The adult Urodele skull is more degenerate than that of other 

 Amphibia, as shown by the small number of both cartilage and 

 dermal bones. There is usually no circumscribed temporal fossa, 

 there being no connexion between maxillary and squamoso-temporal 

 regions.^ The cartilage bones include a pair of exoccipitals bearing 

 condyles. These bones are usually separated by cartilage above and 

 below, no basi- or supraoccipitals ossifying, but they fuse above the 

 foramen magnum in a few genera, and occasionally below it. A pro- 

 otic, the only ossification in the otic capsule, forms in the anterior 

 cupula and extends back on the ventral surface of the capsule, fusing, 

 except in Perennibranchs, with the exoccipital, Ihe resulting bone 

 being usually called the petrosal, though differing from the mamma- 

 lian petrosal. In the interorbital region are two (primitively) paired 

 bones extending forwards to the nasal region and usually including 

 the optic foramen, hence they are orbitosphenoids, though often 



1 In Ranodon and the larva of Cryptobranchus the pterygoid cartilage is continuous 

 with the anterior chondrocranial wall. In Anaides it reaches the ma.xilla. Diemictylus 

 and Triton have a fossa bounded laterally by a bar from the postfrontal which meets the 

 squamosal behind. 



