CETACEA 22$ 



Anatomy of Duyong : Everard Home, Phil. Trans. 1820, p. 315 ; Owen, Proc. 

 Zool. Soc. 1838, p. 29. Placenta of do.:W. Turner, Trans. Roy. Soc. Edin. 

 vol. xxxv. (1889). Manatee: W. Vrolik, Bijdragen tot dc Dicrkundc, 1851; 

 J. Murie, "On the Form and Structure of the Manatee," Trans. Zool. Soc. Lond. 

 vol. viii. p. 127, 1872, and "Further Observations on the Manatee," Ibid. vol. 

 xi. p. 19, 1880 ; A. H. Garrod, "Notes on the Manatee recently living in the 

 Zoological Society's Gardens," Ibid. vol. x. p. 137, 1875 ; H. C. Chapman, 

 "Observations on the Structure of the Manatee," Proc. Acad. Nat. Sciences of 

 Philadelphia, 1875, p. 452 ; A. Crane, "Notes on the Habits of the Manatees in 

 Captivity in the Brighton Aquarium, " Proc. Zool. Soc. Lond. 1881, p. 456. 

 Extinct Sirenia : Gervais, Journal de Zoologie, torn. i. p. 332, 1872. R. Lydek- 

 ker, Catalogue of Fossil Mammalia in the British Museum, pt. v. 



Order CETACEA. 



This is perhaps the most distinctly circumscribed and natural 

 of all the larger groups into which the class is divided. 



The external form is fish-like, the body being fusiform, passing 

 anteriorly into the head 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. 



The head is generally large, in sonie 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 ovoid paddles, encased in a continuous integument, show- 

 ing no external sign of division into arm, fore arm, and manus, or of 

 separate digits, and without any trace of nails. There are no traces 

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

 smooth and glistening, and devoid of hair, although in many species 

 there are a few fine bristles in the neighbourhood of the mouth, 

 which may either persist through life, or be present only in the 

 young state. Immediately beneath the skin, and intimately 

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

 mesh of areolar 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 a compressed median dorsal 

 tegumentary fin is present. The eye is small, and is not provided 

 with a nictitating membrane or true lachrymal apparatus. The 

 external auditory meatus is a very minute aperture in the skin 

 situated at a short distance behind the eye, and there is no vestige 

 of a pinna. The nostrils open either separately or by a single 

 crescentic valvular aperture, not at the extremity of the snout, but 

 near the vertex of the head. 



15 



