684 



MANUAL OF ZOOLOGY. 



is remarkable as possessing upper and lower canines in addi- 

 tion to molar and incisor teeth. The Miocene and Pliocene 

 deposits of Europe have yielded remains of numerous Sireni- 

 ans belonging to the genus Halitherium, in which there are 

 tusk -like upper incisors (as in Halicore), combined with en- 

 amelled molars (as in Manatus}, and in which a rudimentary 

 femur is attached to the pelvis. Re- 

 mains of Rhytina occur in the Post- 

 pliocene of Siberia. 



ORDER V. CETACEA. In this order 

 are the Whales, Dolphins, and Por- 

 poises, all agreeing with the preceding 

 in their complete adaptation to an 

 aquatic life (figs. 384, 386). The body 

 is completely fish-like in form; the ante- 

 rior limbs are converted into swimming- 

 paddles or "flippers ;" the proximal 

 bones of the fore-limbs are much reduced 

 in length, and the succeeding bones are 

 shortened and flattened, and are enveloped 

 in a tendinous skin, thus reducing the 

 limbs to oar-like fins, the phalanges of 

 some of the digits being sometimes in- 

 creased in number (fig. 381); there are 

 no external ears ; the posterior limbs are 

 completely absent ; and there is a power- 

 ful, horizontally -flattened, caudal fin, 

 sometimes accompanied by a dorsal fin 

 as well. In all these characters the 

 Cetacea agree with the Sirenia, except 

 in the one last mentioned. On the 

 other hand, the nostrils, which may be 

 single or double, are always placed at the 

 top of the head, constituting the so-called 

 "blow-holes" or "spiracles ;" and they 

 are never situated at the end of a snout. 

 The body of the adult is in general com- 



bTglts"; r~Rad~ius; u uina; pletely hairless. The testes are retained 

 fif^hTmclfpaf First and throughout life within the abdomen, 

 and there are no vesiculae seminales. 



The teats are two in number, and are placed upon the groin. 

 The head is generally of disproportionately large size, and is never 

 separated from the body by any distinct constriction or neck. The 

 lumbar region of the spine is long, and, as in the Sirenia, 

 there is no sacrum, and the pelvis is represented by a single 



Fig. 381. Hand of Round- 

 headed Dolphin. I V, 



