TYPES OF MOLAR TEETH OF MAMMALIA EDUCABILIA. 89 



But it will be more than this ; it cannot be far removed from the primitive 

 carnivore and the primitive quadrumane. The carnivora are all modified buno- 

 donts, and the lower forms (Ursus Procyon^ e. g.) are pentadactyle and plantigrade. 

 As to the Quadrumana, man himself is a pentadactyle plantigrade bunodont. 

 This view has been already expressed, as follows: "The type of Tomitherium^ 

 already described, evidently stands between lemnrine monkeys and such small 

 allies of Palceotheriida with conic tubercular teeth [Oligotonms, Orotherium, etc.), 

 and which abound in the Eocenes of Wyoming. . . . The dentition of the two 

 types is, indeed, but little diflerent in the Quadrumanous and Ungulate types 

 respectively, being a continuous series of I. 1 or 2 ; C. 1 ; P. m. 3 — 4 ; M. 3 ; the 

 canines but moderately developed."* Such a hypothetical type might be expressed 

 by the name BunotheriidcE, with the expectation that it will present subordinate 

 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 pro- 

 portions, and the incisors in their number. 



In respect to the limbs proper, neither the Quadrumana nor Carnivora attain to 

 the specialization seen in the Artiodactyla and Perissodactyla, 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 dentition, more of the 

 characteristics of the primitive Biinotherium, than any other line of descent of the 

 Manunalia Ediicahilia. It even exhibits a retrogression, in the transition from the 

 anisognathous Tomitherium to the genus Ho7no, 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 advanced, viz., in the number of convolutions and extent of the cere- 

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



* Hayden's Geological Survey of Montana, etc., 1872, p. 645. 



Note. — The extinct genera of American formations alluded to in this paper, have been mostly- 

 brought to light through the explorations of the Territories under Dr. F. V. Hayden, U. S. 



Geologist. 



23 



