328 SCOTT. [Vol. V. 



short. The great trochanter is low, massive, and rugose in 

 front, behind it rises into a high, stout hook, which projects far 

 above the head; the digital fossa does not invade the shaft, but 

 is formed by the recurved edge of the trochanter. The second 

 trochanter is a long, rugose, and prominent ridge, and the third 

 is moderately developed. The distal condyles, of which the 

 outer is considerably the larger, are rather small and do not 

 project strongly backward ; the groove separating them is wide 

 but shallow. The rotular trochlea is broad and shallow, with 

 edges which are sharp and of nearly equal height. A long 

 depression runs up the shaft above the trochlea. Above the 

 external condyle, on the posterior side of the shaft, there is a 

 deep pit for the plantaris muscle. In Anchitherinm (de Blain- 

 ville, Palceotheriam, PI. VII.) the femur is very like that of the 

 American genus, but is somewhat stouter and straighter, and 

 more equine in the details of construction. 



In the horse, the femur has become very much stouter, and 

 all the processes for muscular attachment more massive. The 

 head is sessile, and the great trochanter approaches nearer to 

 it, and the pit for the round ligament is much larger. These 

 changes, as Kowalevsky has pointed out, involve to a con- 

 siderable degree the loss of rotatory movements, and the con- 

 fining of the motion of the femur to the vertical plane. The 

 condyles are much more massive and prominent ; the trochlea 

 is oblique to the long axis of the shaft, and its inner border 

 greatly elevated and enormously thickened. 



The tibia (PI. XXIII., Figs. 32, 33) of Mesohippus is long and 

 very slender, and the shaft has a slight sigmoid curvature. The 

 femoral facets are slightly concave and are placed obliquely to 

 the long axis of the bone, inclining downward and backward. 

 The cnemial crest is long and massive, and has the usual deep 

 tendinal sulcus on its outer edge. The distal end is quite 

 narrow, and the astragalar facets are deep and very oblique in 

 position, with a high intercondylar ridge, which is more promi- 

 nent behind than in front ; the inner malleolus is only moder- 

 ately developed. 



The proximal end of the fibula is not preserved in any of the 

 specimens ; the distal end is sometimes co-ossified with the 

 tibia, as is also a considerable portion of the shaft ; in other 

 specimens it is free. This end is expanded to form a stout 



