FINS OF WHALES 4 I 



on p. 196. The only mammal which appears to have the proper 

 five bones in the distal row of the carpus corresponding to the 

 five metacarpals is Hyperoodon, where this state of affairs at least 

 occasionally occurs. The final bone of that series, the unciform, 

 seems to represent two bones fused. Very often the carpus 

 is reduced by the fusion of certain of the carpal bones ; thus 

 among the Carnivora it is usual for the scaphoid and the lunar 

 to be fused. It is interestingly significant that these bones retain 

 their distinctness in the ancestral Creodonts. In many Ungulates 

 the trapezium vanishes. The reduction of the toes in fact implies 

 a reduction of the separate elements of the carpus. 



As to the digits of the mammalian hand, the greatest number 

 is five, the various supplementary bonelets known as prepollex 

 and postminimus being, it is now generally held, merely supple- 

 mentary ossifications not representing the rudiments of pre-existing 

 fingers. They may, however, bear claws. 1 The number of 

 phalanges which follow upon the metacarpals is almost constantly 

 three in the mammals, excepting for the thumb, which has only two. 

 This is highly characteristic of the group as opposed to reptiles 

 and birds, and the increase in the number of these bones in the 

 Whales and to a very faint degree in the Sirenia is a special re- 

 duplication, which will be mentioned when those animals are 

 treated of. 



The Pelvic Girdle. The pelvic girdle or hip girdle is the 

 combined set of bones which are attached on the one hand to 

 the sacrum and on the other articulate with the hind -limb. 

 Four distinct elements are to be recognised in each " os inno- 

 minatum," the name given to the conjoined bones of each half of 

 the entire pelvis. These are : the ilium, which articulates with 

 the sacrum ; the ischium, which is posterior ; the pubis, which is 

 anterior ; and finally, a small element, the cotyloid, which lies 

 within the acetabular cavity where the femur articulates. The 

 epipubes of the Monotreme and the Marsupial are dealt with 

 elsewhere (see p. 116) as they are peculiar to those groups. 



Professor Huxley pointed out many years since that while 

 the Eutherian Mammalia differ from the reptiles in the fact that 

 the axis of the ilium lies at a less angle with that of the sacrum, 



1 Horny matter is apt to be formed upon extremities ; instances which are well 

 known are the "claws" upon the tail of the Lion and Leopard and the Kangaroo 

 Omjchogale. For an account of the first see Proc. Zool. Soc. 1832, p. 146. 



