No. 3.] OSTEOLOGY OF MESOHIPPUS AND LEPTOMERYX. 3 1 9 



there any indication of the bicipital tubercle at the bottom of 

 the groove. The shaft is slender and slightly curved in a 

 sigmoid shape ; in the middle it is of nearly circular section, 

 below this transversely oval, and proximally it is also oval, with 

 the long axis directed from before backward. The deltoid ridge 

 is prominent and rugose and runs far down on the shaft, form- 

 ing, however, no projecting hook ; the supinator ridge is distinctly 

 marked, but short. The anconeal fossa is very small, but deep, 

 and penetrates the shaft to form the supra-trochlear foramen. 

 The distal end is but little expanded transversely, and the troch- 

 lea is set obliquely to the long axis of the shaft ; it is also of con- 

 siderably greater vertical height internally than externally. The 

 inner condyle is broad on the anterior face, but becomes much 

 narrower on the distal and posterior sides ; the intercondylar ridge 

 forms a broad and thick rounded prominence. The external con- 

 dyle is almost confined to the anterior face, hardly descending at 

 all upon the distal surface ; its outer portion projects laterally and 

 is flared in a peculiar manner, forming with the corresponding sur- 

 face on the radius a joint which allows an extraordinary degree 

 of flexion. The obliquity of the trochlea has the effect of throw- 

 ing the radius outward during flexion ; otherwise the arrange- 

 ment of facets is such that the two bones could be brought into 

 contact through almost their whole length without dislocation. 



The epicondyles are but feebly developed, the external one 

 being hardly indicated, the internal one somewhat larger and 

 more prominent. The inner side of the distal end has a con- 

 siderably greater antero-posterior depth than the outer, so that 

 when the bone is viewed from the side the internal margin of 

 the anconeal fossa is seen to project behind the outer margin, 

 but much less decidedly than in Equus. 



The humerus of Anchitherium is very similar to that of Meso- 

 hippus, but more equine in construction. The shaft is rather 

 stouter, and the deltoid ridge more prominent, an incipient hook 

 being plainly indicated. The external tuberosity is considerably 

 reduced in size, not extending so far toward the medial line. 

 The internal tuberosity \s also smaller, and the bicipital groove 

 much wider and shallower, and has moved toward the outer 

 side ; the beginning of the bicipital tubercle is likewise clearly 

 shown. The distal end is, according to Kowalevsky, thoroughly 

 hippoid in character, and so far as can be judged from his 



