THE MANATIS AND DUGONGS. 165 



of a greenish tinge at the base. In the males also the dewlap is more 

 developed, while in both sexes the limbs are relatively shorter and the 

 colour is blacker. Gayals' are kept ia a semi-domesticated state in Assam, 

 Chittagong, and other parts of north-eastern India, but occur wild in the 

 interior of the Tenasserim provinces of Burma. From both the above, the 

 smaller animal from Burma, Java, Balli, and Lombok known as the 

 banteng (B. banting), differs by the more rounded horns, the slight develop- 

 ment of the ridge on the back, the white patch on the rump of both sexes, 

 and the reddish-brown colour of the body of the cows. 



Lastly, the true, or Taurine oxen are represented by the common ox 

 (B. taunts) and the Indian humped cattle (B. indiaus), both of which are now 

 known only in the domesticated state, although it is possible that the half- 

 wild cattle of certain British parks may be the mora or less modified direct 

 descendants of the old English aurochs, as the wild os was originally called. 

 In this group the spinal ridge characterising the gaur and its allies is absent; 

 the horns are cylindrical, with their tips inclined backwards, and are placed 

 at the very extremity of the highest ridge of the skull ; while the forehead is 

 flat, and the whole skull much elongated. The tail also is larger, reaching 

 below the hocks ; and the hoofs are large and rounded, instead of being 

 narrow and pointed. Probably the original colour of the aurochs was 

 reddish. 



ORDER YII.— SIRENIA. 



The Manatis axd Dugongs. 



This and the following order of mammalj differ from all those hitherto 

 described in that all their members are adapted for a permanently aquatic 

 life — that is to say, they never voluntarily leave the water, as do the seals 

 during the breeding-season. Accordingly, their bodies have assumed a more 

 or less completely fish-like form, with little or no traces of a distinct neck ; 

 while the fore-limbs are modified into paddle-like flippers, the hind-limbs 

 are completely wanting externally, and the tail forms a flattened paddle lying 

 horizontally in the water. Structural evidences clearly show that both groups 

 are descended from terrestrial mammals ; and as these creatures have to 

 come to the surface periodically for the purpose of breathing, the horizontally- 

 expanded form of the tail-fin is sufficiently obvious ; such an organ being 

 admirably adapted, by means of a few powerful strokes, to bring its owner 

 rapidly to the surface. In fishes, on the other hand, which breathe the 

 atmospheric air contained in water by means of their gills, there is no 

 necessity for such periodical visits to the surface, and the tail-fin is accord- 

 ingly expanded in the vertical direction, thus forming a most efficient 

 propeller for progression in a horizontal plane. 



The manatis and dugongs, forming the present order, constitute a very 

 small group of mammals, all of which may be included in the single family 

 Manatidce. Having the general fish-like bodily conformation alluded to above, 

 the sirenians, as members of the present group are collectively termed, 

 diffbr in many important respects from the whales and porpoises. One 

 marked point of distinction ia to be found in the circumstance that the body, 



