278 THE STRUCTURAL EVIDENCE OF EVOLUTION. 



heel belonging to all the lower and primitive Carnivora which is 

 wanting from the sectorial of the adult cat. Moreover, in complex 

 teeth, the different stages of wear represent primitive conditions 

 of the same animal, elsewhere preserved to us in extinct adult 

 genera and species. 



Forms which violate the definitions of the orders above given 

 are also well known. Thus Mesonyx, with the skull and denti- 

 tion of a carnivore, has the separate scaphoid and lunar bones and 

 flat claws or hoofs of an ungulate. Calamodon has the molars 

 of an ungulate, the incisors of a rodent, and claws resembling 

 somewhat those of a carnivore. Uintatlierium has feet partly like 

 an elephant, and teeth of a tapir. 



I have referred the Mammalia with five and four toes, the full 

 number of distinct tarsal and carpal bones, which form interlock- 

 ing series, and in which the tread is plantigrade, to a new order 

 called the AmUyjJoda. These represent the primitive type of the 

 higher Mammalia with convoluted brains, etc., but present much 

 variation in the constitution of the teeth. From the latter have 

 come off not only the three hoofed-orders represented by the ele- 

 phant, the horse, and the ox, but the origin of the Carnivora and 

 Quadrwnana is scarcely distinguishable from it, if at all ; while 

 there is little doubt that the natatory Sireniaii order was derived 

 from it by a process of degradation, chiefly of the extremities, in 

 connection with the assumption of an aquatic life. The mana- 

 tee, of which a fine example may now be seen in our zoological 

 gardens, represents this division. 



The relation of man to this history is highly interesting. Thus 

 in all general points his limbs are those of the primitive type so 

 common in the Eocene. He is plantigrade, has five toes, separate 

 carpals and tarsals ; short heel, rather flat astragalus, and neither 

 hoofs nor claws, but something between the two. The bones of 

 the forearm and leg are not so unequal as in the higher types, and 

 remain entirely distinct from each other, and the ankle-joint is 

 not so perfect as in many of them. In his teeth his character is 

 thoroughly primitive. He possesses, in fact, the original quadri- 

 tuberculate molar with but little modification. His structural 

 superiority consists solely in the complexity and size of his brain. 

 The forms of the quadrumanous order, while agreeing with each 

 other in most respects, display the greatest range of brain struct- 

 ure, and show that while they have made but little progress since 

 the Eocene in perfection of organization of the skeleton, they 



