No. 3] OSTEOLOGY OF MESOHIPPUS AND LEPTOMERYX. 307 



The jugal is quite long and slender, its posterior portion 

 reaching back nearly to the glenoid cavity : it extends, however, 

 but little upon the face, very much less than in the horse, and 

 the masseter surface is but feebly developed. As a whole, the 

 zygomatic arch is decidedly different from that of Equus, being 

 longer, much more slender and compressed. These differences 

 are due in part to the changed position of the orbits, and in part 

 to the increased relative importance of the masseter muscle in 

 the modern species. 



The parietals are long, but narrow ; anteriorly they diverge 

 strongly to receive the posterior projections of the frontals ; the 

 sagittal crest is short and inconspicuous, but longer and more 

 prominent than in the horse ; anteriorly the ridges diverge and 

 form a narrow triangular area. Near the posterior portion of 

 the suture with the squamosal, the parietal is perforated by a 

 number of large venous foramina : in the horse these foramina 

 are situated in the squamosal, are more scattered, and extend 

 farther forward. 



The frontals are very long, but rather narrow ; their shape is 

 much as in the horse, but the forehead is narrower and slightly 

 concave. The frontal sinus is but little developed, and does not 

 extend over the brain at all. The fronto-nasal suture is nearly 

 straight, but in' the median line the frontals send forward a nar- 

 row tongue, which is wedged in between the diverging nasals. 

 The cranium is quite sharply constricted behind the orbits. The 

 post-orbital processes are long and slender, with rugose edges ; 

 there is no trace of any corresponding process from the 

 zygomatic arch. The superior rim of the orbit is more promi- 

 nently projecting in some specimens than in others, and in the 

 former there are two small supra-orbital foramina ; in the latter 

 the foramen is represented by a notch at the anterior base of 

 the post-orbital process. 



The lachrymal is quite large, and though smaller than in the 

 existing genus, extends well up on the face and articulates su- 

 periorly with the nasal as well as the frontal ; in front of the 

 orbit there is a pit or depression, which is partly upon the lach- 

 rymal, but more extensively upon the maxillary. This pit is 

 very much deeper in some specimens than in others, though 

 this difference may be a sexual one, as I have reason to believe 

 is the case in Oreodon. There is an obscure lachrymal spine 



