Order CETACEA. 



Whales, dolphins, arid porpoises constitute an order differing 

 widely, both in form and structure, from all land-mammals. They 

 were at one time supposed to have some affinity with the Carnivora, 

 but Flower has shown that the relationship is doubtful, and that 

 Cetaceans are probably more nearly allied to some of the primitive 

 Ungulates than to any other Mammalia. 



The Cetacea are modified for a purely aquatic life and their 

 external form much resembles that of Fishes. There are no 

 external hind limbs, whilst the tail is flattened and expanded into 

 lobes, known as flukes, so as to resemble that of a fish in outline, 

 though the expansion is horizontal instead of vertical. The 

 anterior limbs are converted into paddles, termed flippers or 

 pectoral fins, the digits being completely united together by skin 

 and destitute of nails. There is in most genera a dorsal fin com- 

 posed of integument. The skin is smooth and hairless, "with the 

 exception of a few bristles round the mouth, generally confined to 

 young animals ; but the body is surrounded, immediately beneath 

 the skin, by a thick layer of fat or " blubber,'' which, like the hair 

 or wool of land-animals, serves to retain the heat of the body. 



The eye is small and the ear-orifice minute ; there is no trace of 

 an external ear. The nostrils open either separately or by a single, 

 generally crescentic, orifice or "blow-hole" much above the 

 extremity of the snout, and in most forms on the top of the head. 

 The mammae, two in number, discharge each by a teat lying in a 

 groove, one on each side of the genital orifice. The testes are 

 abdominal, the uterus is bicornuate, the placenta non-deciduate 

 and diffuse. 



The peculiarities of the skeleton are too numerous for any 

 except the most important to be here mentioned. The bones 

 generally are spongy in texture, the cavities being filled with oil. 

 The skull is greatly modified and consists of a short, almost round 

 brain-case, and of a more or less elongate rostrum. The cervical 

 vertebrae are often partially or wholly anchylosed. There is no 

 sacrum. The mode of attachment of the ribs to the vertebra is 

 more or less peculiar, and presents modifications characteristic of 

 the different families. There are no clavicles. The radius and 

 ulna are distinct, and are flattened, as are all the bones of the 

 wrist and hand. The digits are 4 or 5 in number, more often the 

 latter, and the phalanges of the second and third digits greatly 

 exceed in number those found in other mammals. A pair of 

 styliform bones represent the pelvis. 



