BETWEEN TYPICAL EEPTILES ANB OTHER ANIMALS. 177 



thougli in Chelonians it is usually a groove. And some mammals, 

 like the Walrus, have a trochanteroid ulnar process prolonged 

 beyond the articulation, after the manner of Chelonians. The 

 distal end of the bone is not more thickened than in those mam- 

 mals which show least trace of an olecranon-pit. 



The mammalian ulna — which is usually behind the radius, and 

 when external to it, as in Carnivora, is external only at the distal 

 end — reminds one of the testudinates in the way in which the 

 bone is compressed from side to side. The young Elephant is 

 comparable to the old Tortoise in the extent to which the ole- 

 cranon process of the ulna is developed. But the best parallel 

 to the bone as a whole is seen in the Manatus australis, if we 

 neglect the combined distal epiphyses, on which both ulna 

 and radius abut. After the plan of the Beaver, the radius is 

 the smaller bone of the two. Perhaps its nearest general re- 

 semblance in form is to the Manatee, where, however, the boue is 

 relatively stouter, and is suturally united to the ulna at the 

 proximal end : at the distal ends the bones similarly touch each 

 other on the inner side. 



The carpus in its two rows reproduces all the elements usu- 

 ally found in the mammal ; and in the Testudines the scaphoid 

 and lunar bones are usually anchylosed as in some Carnivores. 



The metacarpal bones are shorter than in any mammal ; the 

 phalanges are as short as those of the Ehinoceros ; and the ter- 

 minal claws resemble those of marsupials in wanting the lateral 

 groove, but differ in being depressed. 



The pelvis is entirly mammalian in the forms and grouping of 

 the bones. The ilium is an elongated massive bone rather less 

 expanded antero-posteriorly at the sacral end than in the Tiger. 

 It contributes, with the pubis and ischium, to form an imperforate 

 acetabulum for the femur, as in mammals ; and its articular surface 

 similarly looks downward. The bone differs from the ilium of mam- 

 mals in being directed according to the reptilian plan, upward and 

 backward from the acetabulum, instead of forward ; in the Testu- 

 dines its direction is more vertical than in the Chelonian type. 

 And it differs from mammals' in not having the sacral end pro- 

 duced beyond the bones with which it articulates. 



The pubes and ischia meet mesially in Testudo as in mam- 

 mals, so as to enclose two large obturator foramina. The 

 ischia are massive behind, transversely truncated, and directed 

 a little downward, with an angular process behind, after the 



