340 SCOTT. [Vol. V. 



The limbs would appear to be quite as long as in the horse, 

 or even somewhat longer, in proportion to the size of the body ; 

 but the relative lengths of the constituent parts are quite dif- 

 ferent in the two genera. The scapula seems to have been 

 rather broad, somewhat as in E. dsinus, and has but a small 

 coracoid process. The humerus is rather long, but with a 

 slender shaft, and with the tuberosities and deltoid ridge and 

 hook not strongly developed. The conformation of the proxi- 

 mal end of the humerus is entirely different from that which 

 occurs in the true Equida, and is closely similar to that of the 

 White River camel, Pcebrotherimn. The ulna and radius are 

 likewise rather long and slender ; the shaft of the former is 

 complete and uninterrupted, though much reduced in diameter ; 

 the two bones are only slightly co-ossified at the distal end. The 

 carpus is decidedly higher, but narrower than in the recent 

 forms, and the arrangement of its component parts quite 

 different, in correlation with the greater number of functional 

 digits. I have seen no complete specimens of the metacarpals, 

 and so their length is conjectural. In width and antero-posterior 

 depth, the third metacarpal is much inferior to that of Equus, 

 and its carpal articulations quite different. On the other hand, 

 the splint bones of the horse are represented by the second and 

 fourth functional digits in Mesohippus, while the fifth digit of 

 the latter is a splint bone. The phalanges are much shorter 

 and very much less massive, and in particular the ungual 

 phalanx of the third digit is very small when compared with the 

 massive bone of recent forms, though its shape is very sug- 

 gestive of equine affinities. 



The pelvis is in general very like that of the horse, but with 

 some marked differences ; the sacral plate of the ilium is some- 

 what more expanded vertically and less everted horizontally ; 

 the crest above the acetabulum is more prominent ; the ischium 

 is somewhat shorter and nearly straight, the posterior end 

 curving upward very much less. The femur has a stout shaft, 

 as compared with that of the humerus, but very slender in 

 proportion to the horse's femur ; it is quite long relatively to 

 that of the latter animal ; the trochanters are much less mas- 

 sive, and the condyles smaller and project backward less 

 strongly ; the rotular trochlea is wider, shallower, and less 

 prominent, and has its two margins of nearly equal height, 



