II FINS OF WHALES 4I 
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.’ 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 aninals 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 hes 
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 
Onychogale. For an account of the first see Proc. Zool. Soc. 1832, p. 146. 
