MERISTIC VARIATION 57 



no bird has shown a trace of v. Added together, this all means 

 that birds have lost digit v from the leg, if they ever possessed it, 

 and iv and v from the wing, with i in a fair way to ultimately 

 disappear from both wing and leg, except when functional in the 

 latter. 



The cat has normally four digits (u to v) on each foot, all 

 with three phalanges, and all furnished with claws. Besides this, 

 I is represented on the fore foot by a pollex (thumb) of two 

 phalanges, and a non-retractile claw, while on the hind foot the 

 hallux (great toe) is rudimentary, consisting of a small bone 

 articulating with the cuneiform but bearing no claw. Of all 

 animals, aside from man, the cat is the most subject to supernu- 

 merary digits, especially on the fore foot. In the great majority of 

 cases the doubling is in the region of digit I. Often the extra mem- 

 ber is shaped, not like its neighbors, but rather as if belonging 

 to the opposite foot, though sometimes it is indifferent. For 

 exhaustive material on this subject, see Bateson, Materials for the 

 Study of Variation, pp. 313-324. 



Speaking generally, the dog tribe has five toes in front 1 (digit 

 i not touching the ground) and four behind (i absent). 



The seal has five digits on all extremities, though the hand is 

 modified into the flipper, and the foot is but slightly functional 

 and evidently well on the road to extinction. 



The whale generally has five digits in front incased in skin 

 to form a flipper, though this number is often reduced to four, 

 and in all cases n and in have more than the usual number of 

 joints. The only traces of a hind limb are a few small bones 

 beneath the sacral region and occasionally a part of a limb. 2 



In the manatee and the dugong the process has gone farther. 

 Though these aquatic mammals have exceedingly serviceable 

 flippers with five digits, yet the hind leg has been entirely lost. 

 The vertebrae in the sacral region are not united, and even the 

 pelvis is represented only by a pair of splint bones, though some 

 fossil forms show a rudimentary femur or thigh bone. 3 



1 Excepting the African hunting dog, which has four (Lydekker, Library of 

 Natural History, p. 496). 



2 This is similar to the loss of wings in the case of the New Zealand apteryx. 



3 Lydekker, Library of Natural History, p. 1156. 



