MAMMALIAN RULE. 255 



regarded as more primitive than those of the dog with four 

 digits, the ox, with two digits, and the horse with one. This 

 at least is the prevailing scientific opinion ; but I shall venture 

 presently, to contest it. Finally, most of the early Tertiary 

 mammals were plantigrade ; that is, they walked on the 

 whole length of the foot, with the heel on the ground ; while 

 most mammals walk on the toes with the heel elevated the 

 "hock" being the heel. This also may be thought a mark 

 of superiority, since man is a plantigrade ; but digitigrade 

 walking sustains the same relation as pentadactylism, to pro- 

 gressive advance. 



Is man then, as a five-toed plantigrade lower than the 

 horse, ox, and dog, which are digitigrade with fewer toes? 

 As a whole, certainly not, since superior brain alone sets him 

 on a pinnacle above them. Is he then inferior in his mem- 

 bral development ? No. Development looks to use, function. 

 Superior development implies more diversified or more dex- 

 trous, functions. Man's limbs compared with any others, 

 show human superiority in a marked degree. What then, is 

 the meaning of the more highly differentiated limbs of most 

 of the mammals? Are we restricted to saying that with act- 

 ually inferior development, they possess superior structures, 

 simply become more highly differentiated structures? That 

 seems to be the prevailing opinion of anatomists. They 

 tell us man's limbs retain the primitive conformation, and they 

 assume that this is an inferior conformation. It is allowable 

 to take the opposite view. Differentiation generally takes an 

 upward course ; but sometimes it takes a downward course. 

 We know a multitude of cases of degenerative differentiation. 

 The paddles and the rudimentary pelvis of the whale ; the flip- 

 pers of the seal ; the rudimentary hind limbs of certain 

 lizards; the footless condition of other lizards and of snakes; 

 the eyeless orbits of cavern fishes, are generally regarded as 

 examples of degeneration. If the obsolescence of a whole 

 limb, as in snakes, is a retrogressive differentiation, then why 

 not the partial obsolescence of a limb, as in four-toed and two- 

 toed mammals ? If the high rank of the equine foot is signal- 



