THE SEA-COWS 



(SIRENIA). 



Fish-like herbivora without dorsal or ventral fins, with a small head and distinct neck, thick lips set with tactile 

 hairs, molars with broad crowns, nostrils at the end of the muzzle, and pectoral teats. 



At the first glance we perceive that the 

 Jbody of these inoffensive herbivorous animals 

 resembles that of the whales in its general 

 form, in the possession of a horizontal tail 

 and of flippers, and in the absence of external 

 ears and hind -limbs. As in some whales, 

 one or two small bones are indeed found 

 buried in the flesh in the pelvic region, repre- 

 senting an undeveloped pelvis; but externally 

 no trace of a hind-limb can be seen. In the 

 skeleton some other characters can be pointed 

 out which these creatures have in common 

 with the whales, such, for example, as the fact 

 of the bone inclosing the inner ear being 

 distinct l from the other bones of the skull, 

 with which it is connected only by sutures; 

 the simplification of the vertebral column, 

 the absence of a sacrum, and so forth. But 

 there the resemblances end, and with respect 

 to all the rest of their organization these 

 animals are quite different from the whales. 

 The head is small, round, well marked off 

 from the neck, the vertebrae of which are 

 not fused together; the eyes are on the 

 upper surface, not low down at the sides; 

 the muzzle is comparatively small, and sur- 

 rounded by swollen fleshy lips, on which are 



1 In most mammals, as in man, that bone is fused witli the 

 temporal bone, forming what is called the petrous portion of the 

 temporal bone. TR. 



set thick and often very long tactile hairs. 

 The nostrils are situated at the end of the 

 muzzle, and lead into nasal cavities of the 

 same structure as in other mammals. The 

 flippers have indeed the form of oars of 

 uniform width, but are longer than in the 

 whales; the digits have only three phalanges 

 each, and all the bones of the flippers are 

 movable on each other by joints, while in 

 the whales, as we have seen, they are firmly 

 united together by fibrous masses. The 

 teeth are differentiated. In the milk-dentition 

 we can distinguish incisors, no canines, but 

 premolars, to which molars of diverse form 

 are afterwards added, these latter being 

 formed in different genera on the type of 

 those of the ungulates. The form of the 

 skull is altogether different from that of the 

 whales, and the same may be said regarding 

 the structure of the brain and the respiratory 

 and circulatory organs. The teats are situated 

 in the pectoral region. Short stiff hairs are 

 scattered over the thick tough skin. 



The sea-cows are often included in one 

 and the same order with the true whales. 

 But when we consider that all the characters 

 which these orders have in common with one 

 another proceed solely from the adaptation 

 to an aquatic mode of life, while the other 

 characters, to be explained by inheritance, 



