SI KENT A. 



729 



the vertebrae (cf. Prototheria), and the small brain with few 

 convolutions. 



The paddle-shaped fore-limbs have, at most, rudimentary 

 nails ; the digits have never more than three phalanges, and 

 the elbow and wrist joints are distinctly movable, whereas 

 in the Cetacea the fore-limbs are more or less stiff from the 

 shoulder. There are no clavicles. The skull is not like 

 that of Cetaceans. The nasals are, at most, rudimentary. 

 There are no canine teeth. There are chevron bones below 

 the tail. There are no hind-limbs. The pelvis is rudi- 

 mentary, and there is no sacrum. In the extinct Hali- 

 therium there was a vestigial femur. 



The small eyes have imperfect eyelids, but have a nicti- 

 tating membrane. In the mouth there are horny crushing 

 plates. The ventricles are separated by a cleft. The 

 uterus is bicornuate. Two teats lie behind the armpits. 

 The placenta of the dugong is zonary, wholly or in great 

 part non-deciduate. The placenta of the manatee has not 

 yet been investigated. 



MANATEE (Manatus). 



Xeck vertebrae reduced to six. 

 Abortive incisors (f ) in both sexes. 



Molars ({-{) six or so at a time, 

 uniform, with square enamelled 

 crowns, and tuberculated trans- 

 verse grinding ridges. 



Premaxillse almost straight. 



Tail rounded. 



Rudimentary nails on ringers. 



Caecum divided. 



M. australis and .!/. senegalensis 

 live in the mouths of great rivers 

 which flow into the tropical 

 Atlantic. 



DUGONG (H ali core). 



The usual seven neck vertebras. 

 Two tusk-like incisors persist in 



the male. 

 Molars (f or , 2 or 3 at a time), 



primitive, with persistent pulps 



and no enamel. 



Premaxillas crooked downwards. 



Deeply notched tail. 



Xailless digits. 



Thick and single caecum. 



H. tabernaculi, E. African coast 

 and Red Sea ; H. dugong, Indian 

 and Pacific Oceans, eastward 

 from the home of the last species 

 to the Philippines ; H. australis, 

 E. and N. Australia. 



The genus Rhytina was toothless, with a slightly crooked snout, 

 small head and arms, and thick naked skin. Steller's sea-cow (R. 

 stclleri) the only known species, from the North Pacific seems to have 

 been exterminated in the last century. The tertiary HaUthcrinm, 

 had traces of hind-limbs. 



