336 



SCOTT. 



[Vol. V. 



than the trochlea, but there is no pit above the latter. The 

 head of metatarsal IV. is decidedly more massive, and the differ- 

 ence in the shape and size of the shaft between this and meta- 

 tarsal II. much more marked (see Kowalevsky, No. 25, PI. II., 

 Fig. 28). 



In Eqitus there are very important changes aside from the 

 great development of the median digit, and the reduction of 

 the lateral ones to splint bones, accom- 

 panied by the loss of their phalanges. 

 The head of metatarsal II. now has the 

 facet for the entocuneiform proximal, and 

 that for the mesocuneiform oblique and 

 anterior. 



The head of metatarsal III. has four dis- 

 tinct facets, three anterior for the meso- 

 and ectocuneiforms and cuboid respec- 

 tively, the latter altogether proximal in 

 position ; the fourth facet is posterior and 

 for the beak of the ectocuneiform, and is 

 separated by a large fossa from the ante- 

 rior surface for that bone. The trans- 

 verse breadth of the posterior facet is 

 very striking as compared with the same 

 structure in Mesohippus. The head of 

 metatarsal IV. is provided with two dis- 

 tinct facets for the cuboid. The distal 

 end of the shaft of the median metatarsal 

 is not produced laterally beyond the troch- 

 lea, and there is no pit above the latter. 

 The phalanges of the pes in Mesohippus 

 appear to be somewhat more massive than those of the manus ; 

 whether they are shorter the available material does not enable 

 me to decide. 



FlG. B. — Equus Bur, helli. 

 Proximal end of left meta- 

 carpus and metatarsus (after 

 Kowalevsky). X \. td! , fa- 

 cet for the trapezoid ; mg 1 , for 

 the magnum; u', for the un- 

 ciform; c', for the ento-; c", 

 for the meso- and c'", for the 

 ectocuneiform; cu', for the 

 cuboid. 



VII. Restoration of Mesohippus (Fig. C). 



The successive genera of the horse series show for the most 

 part a steady increase in size from the tiny Hyracotherium of 

 the Wasatch Eocene to the great animals of Post-Pliocene times. 

 Mesohippus, however, has not reached a large stature, advancing 



