e 



90 



ill tlie union of llie rami of tlie jaw at the sj'inpliysis, in the small size of the 

 condyle, in the crowded condition of the teeth, and iu the number of incisors, 

 canines, and true molars, wliich are also nearly alike in constitution. Notharc- 

 tus possesses one more premolar and the othei's have a pair of fangs. The 

 resemblance is so close that but little change would be necessary to evolve 

 from the jaw and teeth of Notharctus that of a modern monkey. The same 

 condition which would lead to the suppression of a first premolar, in continu- 

 ance would reduce the fangs of the other premolars to a single one. This 

 change, with a concomitant shortening and increase of depth of the jaw, would 

 give the characters of a living Cebus. A further reduction of a single premo- 

 lar would give rise to the condition of the jaw in the Old World apes and man. 



IIIPPOSYUS. 



HlPPOSYUS FOEMOSUS. 



Several small fragments of jaws with teeth, discovered by Dr. Carter in 

 the vicinity of Fort Bridger, are suspected to belong to a different genus of 

 pachyderms from any of those indicated in the jjreceding pages. One of the 

 specimens consists of an upper-jaw fragment with the molars in a mutilated 

 condition. The first and second molars are the l)est preserved, and are rep- 

 resented in Fig. 41, Plate VI, magnified three diameters. The first one is 

 nearly entire, but in the figure is represented in a restored condition by the 

 addition of the antero-external angle marked l:)y the zigzag black line. 



The upper molars bear a general resemblance in the construjction of their 

 crowns to those of Anchitherium. The outer lobes are like those in the lat- 

 ter, but have their outer buttress-like ridges proportionately thicker. The 

 antero-intei-nal lobe is larger than that behind and conjoins it. In Anchitherium 

 the inner lobes are nearly equal and isolated from each other. The antero- 

 median lobe, as existing in Anchitherium, in the present fossil is completely 

 connate as part of the antero-internal lobe, and the postero-median lobe of 

 the former is nearly obsolete, or appears as a mere rudiment in Hipposyus. 

 A strong basal ridge incloses the crown in front, behind, and internally, but 

 is absent in Anchitherium in the latter position. 



The measurements of the specimen are as follows: 



Lines. 



Space occupied by the three molars T^i 



Breadth of first molar ^i 



Breadth of second molar ' oa 



■"4- 



Breadth of third molar , 2i 



Width of first molar transversely 3i 



