FOSSIL HORSE REMAINS FROM IDAHO — GAZIN 313 



the astragalus and calcaneum is directed downward and more inward 

 than in the fossil material. In other Equus specimens the inward 

 projection of this facet is not so pronounced. 



The posterior margin of the navicular in many cases is more 

 deeply notched than in the E. grevyi material, noticeably in the 

 outline of the facet for the astragalus as this surface extends well 

 out onto the postero-iuternal prominence. On the distal surface the 

 smaller facets are irregular in size and shape and may or may not be 

 confluent with the larger facet for the external cuneiform. 



The fused internal and middle cuneiforms present an irregular 

 shape and vary in size among individuals. The anterior and posterior 

 portions of the proximal facet for the navicular may be broadly con- 

 fluent or nearly separate. On the distal surface the facets for the 

 second metatarsal may be distinct or meet at a sharp angle. The size 

 of the facet for the third metatarsal is variable though generally small. 

 No persistent differences were observed in comparison with modern 

 material. In one of the fossil skeletons the internal and middle cunei- 

 forms were found separated, as was also observed in one of the recent 

 individuals of E. caballus. 



On the external cuneiforms the proximal facets for the navicular 

 are commonly separated but those on the distal surface for the third 

 metatarsal are generally continuous between the anterior and poste- 

 rior portions. In nearly every specimen the external cuneiform shows 

 a facet postero-internally for articulation with the second metatarsal. 

 In Equus caballus articulation between these bones is much less com- 

 mon, and none of the material at hand shows evidence of it, although 

 two of the three observed pairs of ectocuneiform bones belonging to 

 E. grevyi show facets for the inner splint. 



On the proximal surface of the cuboid the width anteriorly across 

 the facets for the astragalus and calcaneum appears narrower in 

 much of the material, and the surface is perhaps more convex trans- 

 versely than in the E. caballus material at hand. Also, the posterior 

 portion of the facet for the calcaneum is not directed inward so notice- 

 ably in most of the fossils. On the distal surface the facet for the 

 fourth metacarpal though varying appreciably in size is almost always 

 undivided. The few E. caballus cuboids observed show the facet for 

 fourth metacarpal divided and with the posterior segment distinctly 

 small. The cuboids in the E. grevyi material more closely correspond 

 to those in the fossil form. 



Metatarsus. — The third metatarsals (fig. 24, B), as in the case of the 

 third metacarpals, show a certain uniformity and correspond nearly in 

 size to that in E. grevyi. The extremes of length differ by about 20 

 mm. The size range is far less than in E. caballus, and the distal artic- 

 ular surface is relatively much narrower transversely and does not 

 extend so far up the posterior surface as in the specimens of that 



