1903.] Gidley, A New Three- Toed Horse. 47^ 



The spine of the yth cervical is comparatively higher than 

 in Eqnns, but more reduced than in McsoJiippns. 



The spines of the anterior dorsals are long and slope back- 

 ward at a greater angle than in Eqnns. 



The spines of the Innibar vertebrae are comparatively high 

 and narrow. The transverse processes of the third lumbar 

 from the sacrum are comparatively long and do not articulate 

 with those of the second lumbar from the sacrum. 



The ribs are remarkably like those of the zebra in form, 

 except the more posterior ones, which are proportionately 

 longer and have a greater curvature. 



The stern nut, which is well preserved in the type specimen, 

 is very characteristic. It is composed of six bony segments, as 

 is usual in the horse, but the ventral keel, so highly developed 

 in the living horses, is entirely wanting, except in the two 

 anterior segments, and it is only weakly developed in these. 

 The ventral surfaces of the third, fourth, and fifth sections are 

 fiat and are widest transversely. The xiphisternum is the 

 largest of the series. The anterior portion of the ventral sur- 

 face is broad, concave, becoming narrower posteriorly where 

 the edges turn upward, making the posterior third of the 

 ventral surface convex. 



The cartilaginous ribs are composed mainly of spongy bone 

 as in the horse, hence are preserved in the type specimen. 



IV, The Fore Limb. 



The scapnla is distinguished from Eqnns by: (i) relatively 

 narrow prespinous fossa; (2) the narrowness of tlie neck; (3) 

 the prominent vertical ridge or thickening of the subscapular 

 area beneath the postscapular border. 



The hnnicrns is widely distinguished from that of Iiqnns by: 

 (i) the depth and narrowness at the proximal and distal ex- 

 tremities; (2) the shallowness of the bicipital groove; (3) the 

 absence of the groove in the lesser tuberosity; (4) the sharp 

 definition of the grooves and convexities of the ulno-radial 

 trochlea. 



The radins is proportionately long and slender and, except 



