8l2 



THE AMERICAN NATURALIST. [Vol. XXXVIII. 



liest representatives are no larger than rabbits. Elephants, 

 rhinoceroses, tapirs, every race about whose ancestry anything is 

 known, exhibit a reduction in size corresponding to the distance 

 back through which we have been able to trace them. The 

 large animals of the early Tertiary are in every case early 

 specializations which have left no descendants. 



2. ^Molar teeth bunodont'' i.e., low crowned, the eroivns 

 composed of a few low broad rounded cones, heavily enamel-cov- 

 ered. The molars are tubercular {crushln<r) teeth, the premolars 

 trenchant (cuttino^), the canines nwderately large {piercing), the 

 Incisors small spa tu late (nipping) teeth. The teeth were 

 arranged in continuous series, except for slight gaps behind 

 the canines. The labors of Cope, Osborn and many other 

 pakuontologists have amply demonstrated this as the primi- 

 tive type of dentition among the Mammalia. Whether we 

 accept the whole of the ^Tritubercular Theory or not, this part 

 of it appears to be beyond question. 



3. — Xeck rather short, slender and flexible, permitting quick 

 and easy turning of the head in all directions. Trunk slender, 



(^nd comparatively flexible. These features characterize all early 

 Tertiary mammals, without exception. 



Tail very long and flexible, ivith strong muscles toivards 

 the base^ and probably prehensible. All primitive Tertiary mam- 

 mals ha\ e remarkably long and strong tails. These differ from 

 those <it the cats and resemble those of the prehensile-tailed 

 monkeys m the greater breadth of the zygapophyses of the 

 pn)\imal caiukil vertebrae and great size and length of 



Shoulder girdle of scapula and clavicle. No indications 

 a separate coracoid have been observed in early Tertiary 

 mammals. l)ut the clavicle was certainly developed in the 

 ancestors of several groups which do not now possess it, and 

 was piu )ah:v generally present in the earliest types. 



- Ilia narrow and rod-like, gluteal muscles long and slen- 

 der. 



7, ~ rppcr members of limbs coniparativelv lorn; and loosely 



