1903.] Gidley, A New Three- Toed Horse. 473 



III. Their shafts taper to very slender proportions, but 

 expand again distally, forming articular ends which support 

 small lateral toes. Compared with Mesohippus and Eqims, 

 metacarpal III is very long and slender. The distal end is 

 keeled entirely around, but is not so strongly developed on 

 the distal surface as in Eqnus. The lateral toes are much 

 shorter than the median toe, their extreme jjoints reaching 

 only to about four fifths the length of the first phalanx of the 

 latter. The terminal phalanx of the median toe, compared 

 with that of Eqnus, is proportionately longer and more com- 

 pressed laterally in front. The palmar surface is heart-shaped 

 in outline, with the apex deeply cleft. The proximal end 

 is moderately high. The articular facet is placed at about 

 the same angle as in Eqnus. Two processes extend outward 

 and backward, one on either side of the articular face. These 

 processes are thin, with rounded edges, and each is perfor- 

 ated by an arterial foramen. 



V. The Hind Limb. 



The femur is slender and the shaft is relatively long. The 

 second and third trochanters are placed relatively nearer the 

 proximal end of the shaft than in either Mesohippus or Eqnus. 

 The groove for the ligamentum patellae is comparatively 

 longer and narrower than in Eqnus. The tibia exceeds the 

 femur in length, but in other respects is like that of Equus. 

 The fibula is as much reduced as in Eqnus. The remnant of 

 the distal end is entirely fused with the distal end of the tibia. 



The tarsus is relatively deeper anteroposteriorly than in 

 Eqnus, but is essentially the same in other proportions. The 

 shallow, irregular pits are beginning to form on the broad, 

 flat facets of the astragalus, navicular, cuneiforms, and the 

 proximal end of metatarsal III, but are, for the most part, 

 only indicated by slight depressions and roughened patches 

 on the bone surface. In Equus these pits are deeper and 

 their boundaries are well defined, though varying greatly in 

 size and form in different individuals. 



The metatarsals are very long and slender, metatarsal III 

 equaling the femur in length. The lateral digits are reduced 



