CETACEA. 155 



Ord. CETACEA. The ^Yllale tribe. 

 Cetie of some. — Mutilata, Owen. 



Anterior feet clianged into fins ; no posterior extremities. Tail 

 horizontal, 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 temperatui'e 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 foetal state of some, 

 and whiskers in one remarkable genus. 



They have spu-acles 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 fi-ee 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 numei'ous phalanges. Two small bones suspended in the flesh near 

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

 absent, but the caudal vertebrfe 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 pleui^a, and between the ribs on each 

 side of the spine. These form a reservoir of oxygenated blood, which 

 supports life 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 



