MOLAR TEETH OF THE MAMMALIA EDUCABILIA. 267 



Ungulate types respectively, being a continuous series of I. 1 or 

 2 ; C. 1 ; P. m. 3 — 4 ; M. 3 ; the canines but moderately devel- 

 oped. "* Such a hypothetical type might be expressed by the 

 name BunotlieriidcB, with the expectation that it will present sub- 

 ordinate variations in premolar, canine, and incisor teeth. The 

 premolars might be expected to differ in the degree of development 

 of the internal lobes, the canine in its proportions, and the incisors 

 in their number. 



In respect to the limbs proper, neither the Quadriimana nor 

 Carnivora attain to the specialization seen in the Artiodactyla 

 and Perissodadyla, for the ulna and fibula are never atrophied 

 nor co-ossified with the radius and tibia, but are always distinct 

 and free ; the only modification of structure in these points being 

 the slight one involved in developing the rotary capacity seen in 

 the higher monkeys. 



Thus the human series preserves in its feet, limbs, and den- 

 tition, more of the characteristics of the primitive Bunotlieriwn 

 than any other line of descent of the Mammalia EducaMlia. It 

 even exhibits a retrogression, in the transition from the anisog- 

 nathous Tomitherium to the genus Homo, where the teeth in the 

 two jaws are exactly alike, as well as in the resumption of the 

 continuity of the dental series after the diastema had prevailed 

 among the higher monkeys. In one respect it has steadily ad- 

 vanced, viz., in the number of convolutions and extent of the 

 cerebral hemispheres and relative size of the brain as a whole. 



Note (Ed. 188fi). — As remarked in a previous note, the discovery of the general 

 characters of the genus Phenacodus in 1881, more than six years after the publica- 

 tion of this paper, demonstrated the truth of the hypothesis here proposed, viz. : 

 that the ancestor of the Mammalia Educabilia was a pentadactyle plantigrade buno- 

 dont. The numerous genera and species allied to Phenacodus have been placed in 

 a suborder Condylarthra. See " American Naturalist," 1884, 790, for an illustrated 

 article on this group. 



* 



Ilayden's " Geological Survey of Montana," etc., 1872, p. 645. 



