398 LAND MAMMALS IN THE WESTERN HEMISPHERE 



downward from the rump to the shoulders; in the fore-arm 

 the two bones were entirely separate and in the lower leg the 

 fibula, though very slender, was still complete. In the manus 

 there were four functional digits, the laterals not very much 

 smaller than the median pair; but in the pes the lateral 

 metatarsals were reduced to mere bony threads, to which small 

 phalanges, in full complement, were attached, making tiny 

 dew-claws. 



With ^Protylopus ends the genealogy of the camels so far 

 as it can be definitively traced, but in the middle of the Bridger 

 stage is found a genus, ^Hvmacodon (family fDichobunidae), 

 which is a probable member of the series. However, until 

 the connecting link can be found in the upper Bridger, this 

 conclusion cannot be demonstrated and ]Homacodon itself is 

 incompletely known. It was a very small animal, even less 

 in size than \Protylopus, and had not yet acquired the seleno- 

 dont molars. These teeth were quadritubercular, i.e. with 

 four principal cusps arranged, in the upper molars, in a square, 

 and with a minute cuspule between each transverse pair, while 

 the lower molars were narrower and' had only the four prin- 

 cipal cusps. The cusps were not conical, as they are in the 

 pigs, but angular and pyramidal, the first step toward the 

 assumption of the selenodont form. The skull was not 

 specifically cameline in appearance, but rather indifferent, 

 as though almost any kind of an artiodactyl might have been 

 derived from it. The feet were decidedly more primitive than 

 those of the Uinta genus, having four functional digits each, 

 perhaps five in the manus. While it cannot be positively 

 stated that \Homacodon was the actual ancestor of ]Protylo- 

 pus, it nearly represents what we should expect that ancestor 

 to be. 



In the lower Eocene (Wasatch stage) lived a tiny creature, 

 ■\Trigonolestes (family fTrigonolestidae), smaller even than ]Hom- 

 acodon of the Bridger, and one of the most ancient and primitive 

 of known artiodactyls, but, unfortunately, still represented only 



