128 



VERTEBRATE SKELETON 



Fossil Urodeles are rare. Lysorophus (fig. 135) from the Permian is appar- 

 ently one, having the general Urodele structure except a median bone behind 

 the parietals, which is without parallel in modern Amphibia. The stegocrota- 

 phic skull suggests the Gymnophiona, but details oppose such association. 

 The four branchial arches and the exoccipital condyles exclude it from the Rep- 

 tilia, though Broih regards it as reptilian because of the participation of the 

 basioccipital in the condyles. 



Gymnophiona. — The skull of the Caecilians recalls with its almost 

 stegocrotaphic roof, the Stegocephals, but there is less resemblance in 

 details. There is a gap, small in Ichthyophis and CcBcilia, larger in 



Fig. 135. — Skull of Lysorophus (Will- 

 iston, '08). eo, exoccipital ; /, frontal; 

 n, nasal: p, parietal; pa, ?proatlas; pf, 

 prefrontal; q, quadrate; so, possible 

 supraoccipital. 



Fig. 136. — Chondrocranium of Ichthy- 

 ophis (Winslow, '98). ch, notochord; e, 

 ethmoid plate; oc, otic capsule; pf, per- 

 ilymph foramen; ps, sphenolateral; t, 

 trabecula. 



Siphonops, between parietal and postfrontal; the bones are fewer 

 than in Stegocephals. Unfortunately no fossils are known; the 

 recent species are tropical. 



The chondrocranium (only the later stages known) is more Urodelan than 

 Anuran (fig. 136). The large basicranial fenestra is traversed behind by the 

 notochord which is absorbed later. The otic capsule is nearly closed medially. 

 Trabecula and sphenolateral are more distinct than in other Amphibia, the 

 ethmoid plate formed by union of the trabeculae is farther forwards, relative to 

 the nasal capsules, than is usual in Amphibia. The pterygoquadrate is small, 

 the larger quadrate part bearing pterygoid and epipterygoid processes, the 

 former not reaching the cranium in front. The quadrate resembles that of 

 Urodeles in its downwards and forwards direction and its articulation with the 

 stapedial stylus. The Meckclian cartilage is noteworthy for the distance it 



