No. 3-] OSTEOLOGY OF MESOHIPPUS AND LEPTOMERYX. 347 



and the walls are composed of very dense, flinty-looking bone. 

 The meatus auditorius is a long tube, with relatively very large 

 diameter, which extends more decidedly backward and less 

 upward than in the tragulines. The postero-external angle of 

 the bulla shows a rather wide and shallow styloid groove. So 

 far as I can interpret the sutures, there appears to be a broad 

 surface of the periotic exposed between the squamosal and the 

 occipital ; but if so, it lies entirely in the occipital plane and not 

 on the side. 



The parietals are very long and form almost the entire roof of 

 the cranium ; they are much longer and narrower than in Trag- 

 ulus. This narrowing is partly due to the fact that the brain 

 itself is narrower, and partly that the squamosals encroach much 

 more upon them. In front of the latter, the parietals send 

 down descending processes to the sphenoids. The sagittal 

 crest varies in length, but is always longer than in the tragu- 

 lines. Anteriorly the parietals diverge somewhat to receive the 

 frontals and are thus rather longer on the sides than in the 

 median line. 



The squamosals are very long and high proportionately, and 

 form most of the side walls of the cranial cavity. The root of 

 the zygomatic process is stouter, but less extended antero- 

 posteriorly, and the process itself is longer and heavier than in 

 Tragulus ; the zygoma rises slightly forward, whereas in the 

 recent genus it descends anteriorly. The glenoid cavity is very 

 different in the two forms ; in the existing type, it is a broad, 

 flat surface, with nothing deserving the name of a post-glenoid 

 process ; in Leptomeryx " its fore part is nearly straight trans- 

 versely, and inclines slightly outward from its inner extremity, 

 and slopes convexly backward and outward into a comparatively 

 deep concavity, bounded behind by a post-glenoid tubercle 

 proportionately stronger than in the deer " (Leidy). The post- 

 tympanic process is also more distinctly developed than in 

 Tragulus. The jugal has a nearly straight course, and is rela- 

 tively a very large bone, with much greater vertical diameter 

 than in Tragulus ; the masseteric crest occupies nearly the 

 same position as in that genus, but is not nearly so well 

 developed. There is quite a long post-orbital process, but it is 

 shorter than in the existing genus, and does not quite reach the 

 corresponding process of the frontal. The lachrymal, on the 



