CETACEANS. 105 



Their external form is fish-like, the body being <e fusiform " or 

 spindle-shaped, passing anteriorly into the head, usually without 

 any distinct constriction or neck, and posteriorly tapering off 

 gradually towards the extremity of the tail, which is provided with 

 a pair of lateral, pointed expansions of skin supported by dense 

 fibrous tissue, called "flukes," forming together a horizontally- 

 placed triangular propelling organ, notched in the middle line 

 behind, with which the animals scull themselves through the water. 

 The characteristic form of the tail is well seen in many of the smaller 

 stuffed specimens in the Gallery, and in that preserved and attached 

 to the great skeleton of the Rorqual, to be spoken of presently. 



The head is generally large, in some species attaining to even 

 more than one third of the entire length of the animal, and the 

 aperture of the mouth is always wide, and bounded by stiff 

 immobile lips. The fore limbs are reduced to the condition of 

 flattened paddles, encased in a continuous skin, showing no ex- 

 ternal sign of division into arm, forearm, and hand, or of separate 

 fingers, and without any trace of nails. There are no signs of hind 

 limbs visible externally. The general surface of the skin is smooth 

 and glistening, and devoid of hair, although in most species the 

 mammalian character of hairiness is just indicated by the pre- 

 sence of a few fine bristles in the neighbourhood of the mouth, 

 which either remain through life, or are to be found only in the 

 young state. Immediately beneath the skin, and intimately con- 

 nected with it, is a thick layer of fat, held together by a dense 

 mesh of fibrous tissue, constituting the " blubber," which serves 

 the purpose of the hairy covering of other mammals in retaining 

 the heat of the body. In nearly all species there is a fin, more 

 or less triangular in shape, composed only of skin and fibrous 

 tissue, near the middle of the back, which, as in the analogous 

 dorsal fin of fishes, assists to keep the animal in an upright posi- 

 tion when swimming through the water. The eye is small ; and 

 the aperture of the organ of hearing extremely minute, and with- 

 out vestige of a pinna or external ear. The nostrils, generally 

 called " blowholes," open separately, or by a single valvular 

 aperture, not (except in the Sperm Whale) at the extremity of 

 the snout, but near the top of the head. 



The bones generally are spongy in texture, their cavities being 



