CETACEA. 155 



Oed. CETACEA. The Whale tribe. 

 Oetce of some. — Mutilata, Owen. 



Anterior feet changed into fins ; no posterior extremities. Tail horizon- 

 tal, flat, continuous with the trunk ; no external ears. 



Cetaceans are distinguished by the fish-like form of their members, and 

 live in seas and large rivers. They are generally bulky animals, with very 

 large heads, tapering bodies, terminated by a broad tail-fin, which is the 

 principal agent in swimming. It is supported by cartilage only. The 

 head is not separated from the body by a neck. The eye is of very small 

 size, and from the great development of their facial bones, appears in 

 some to be placed nearly in the middle of the body. Their skin is thick 

 and intimately mixed with fat forming the blubber, which serves to preserve 

 the warm temperature of the body in the cold seas they frequent, and 

 at the same time renders them light. Their skin is usually devoid of 

 hair except a few bristles in the fsetal state of some, and whiskers in one 

 remarkable genus. 



They have spiracles or external nostrils, sometimes on the fore part of 

 the nose, but usually on the top of the head, which can be closed by a 

 conical stopper or valve. The cervical vertebrae are free in some, more 

 or less anchylosed in others. The sternum is short and wide. The ribs 

 are much curved, and very few of them join the sternum. They have no 

 clavicles. The anterior limbs are completely enclosed, forming a fin, but 

 contain the usual bones of the arm of vertebrate animals, sometimes with 

 very numerous phalanges. Two small bones suspended in the flesh near 

 the anus are the only vestiges of posterior extremities. The sacrum is 

 absent, but the first caudal vertebrse are distinguished from the lumbar 

 by the presence of a series of inferior small V-shaped arches. 



They have large brains with many and deep convolutions. The arteries 

 are infinitely convoluted, and vast plexures of vessels filled with oxygenated 

 blood occur under the pleura, and between the ribs on each side of the 

 spine. These form a reservoir of oxygenated blood, which supports Ufe 

 whilst their respiration is suspended under water. 



The petrous portion of the temporal bone, which contains the internal 

 ear, is separated from the rest of the head. The organ of hearing is of 

 great delicacy. Their sense of smell is little developed. They are either 

 edentulous, or the teeth are of one kind, simple in form, and one set only 



