BETWEEN TYPICAL EEPTILES AND OTHEK ANIMALS. 185 



§ 8. The Urodelan Characters of Ghelonians. 



There is a general resemblance of form between the crania of 

 Chelys mainmata and the Menopome. The quadrate and squamosal 

 bones are as firmly fixed in the skull as in Ghelonians, and in the 

 Mammata are similarly directed more outward than downward. 

 The maxillary and prefrontal make the front and base of the 

 orbit ; in Salamanders its hinder part is not circumscribed with 

 bone. The pterygoid in the Menopome is a large bone like that 

 of the Mammata, and the bones are mesially parted from each 

 other as in Trionyx ; only the separation is made by the basi- 

 temporal in the Menopome, and not by the basisphenoid. The 

 pterygoid in both similarly meets the quadrate. In Tritons the 

 quadrate bone is directed forward as in the extinct Ornitho- 

 sauria. 



The humerus of the Grerman Salamander has a digital process 

 at the proximal end, which is not likely to recall the ulnar pro- 

 cess in a Chelonian. The radius is proportionally a very large 

 bone, and is greatly expanded at the distal end. The ulna is 

 sufficiently similar to that of marine and freshwater Chelonia to 

 suggest comparison. 



The carpals in Menopoma have no existence ; in the Salamander 

 they are well ossified, and, though very different, are more sugges- 

 tive of the marine Chelonia than of the other types. 



The pubis is unossified in the Urodela ; and the ischia are large 

 reniform bones unlike those of any Chelonian ; but the ilium 

 appears to be similar. 



The femur, though having a hemispherical proximal articulation 

 and a widened distal end, has proximally a digital trochanter 

 unlike that of a Chelonian and more suggestive of an Iguanodont 

 Dinosaur's. 



The tarsals differ in the same way as the carpals ; and the 

 compressed dicebox-shaped metacarpals and phalanges are in- 

 termediate in elongation between the marine and land types of 

 Ghelonians. 



Usually Batrachian bones differ from those of Ghelonians in 

 being hollow, and in having epiphyses. 



