CETACEA 225 
Anatomy of Dugong :—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). Janatee:—W. Vrolik, Bijdragen tot de Dierkunde, 1851 ; 
J. Murie, ‘‘On the Form and Structure of the Manatee,” Z'rans. Zool. Soc. Lond. 
vol. viii. p. 127, 1872, and ‘‘ Further Observations on the Manatee,” Jbid. 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, tom. i. p. 832, 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 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 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 
