SKELETON OF SIRENIA. 429 



support a metacarpal and six phalanges. All the digits in the 

 entire Cetacean are enveloped in a common fold of integument. 

 The increase of the phalanges of certain digits beyond the number 

 three is a remarkable instance of departure from the mammalian 

 type and of affinity with the extinct enaliosaurs and fishes. 



In the DelpliinidcB there are a pair of pelvic bones larger in 

 males than females, chiefly subserving the origins of the ^ erectores 

 penis' and 'clitoridis'; and which, therefore, I regard as ischial 

 bones. In a female Hyj^eroodon 28 feet long, each ischium 

 was 41 inches long, straight, subtriedal, 8 lines in diameter. In 

 BalcBna mysticetus there is, besides the ischium, fig. 192, e;?, a 

 smaller, more slender and curved ossicle, which, being anterior 

 to it, seems to represent a pubis, ib. 64 : the junction of the two 

 bones expands into a surface, representing the acetabulum, to 

 which is ligamentously suspended a bone of similar length to the 

 pubis, but thicker, and expanding, with some flattening, to a 

 transversely extended convex surface, like that at the distal end 

 of a chelonian femur ; ib. 65 : to which is suspended a smaller 

 rudiment of a tibia, 66. This is the simplest condition of the 

 limb, or appendage, of the pelvic arch known in the Mammalian 

 class. ^ There is no outward indication of it in the Whale. The 

 little bones, of the relative size to the rest of the skeleton as 

 shown in fig. 159, p. 280, are suspended beneath the last two 

 lumbar vertebrae, which may thus be regarded as answering to 

 the sacral in quadrupeds. 



§ 185. Skeleton of Sirenia. — In this class of marine Mammals 

 the hind limbs are absent, as in Cetacea, and the pelvic bones, 

 where best developed, as in fig. 292, s, h, retain the size and 

 shape of the small contiguous costal arches. The texture of 

 the bones is denser, the neck, though short, is longer than in 

 the Cetacea, and the vertebra? are distinct: but the chief dif- 

 ferences are found in the relative size and structure of the skull, 

 and in the better developement of the bones of the pectoral limb, 

 the digits of which are not composed of more than the normal 

 mammalian number of phalanges (compare fig. 292 with fig. 159, 

 p. 280). The known existing representatives of the Sirenian 

 order are the Dugongs {Ilalicore) and the Manatees {Manntus): 

 the latest extinct form is the edentulous Sirenian, called ^ Steller's 



' The bones described and fif^urcd in cli. t. v. p. 236, pi. xxvi,, figs. 24 and 

 25, were not seen in situ by Cuvier, but are described as pelvic bones, on the au- 

 thority of M. Delalande, the Articulator. The discoverers of the rudimental hind 

 limbs, and authors of lxv', observed the pelvic bones of the whale in situ (p. 151, 

 tab. II.). 



