312 SCOTT. [Vol. V. 



Another well-preserved specimen of a Mesohippas brain-cast 

 was obtained by the Princeton Expedition of 1890, which pre- 

 sents some differences from the one figured by Osborn. This 

 brain was of a larger animal (perhaps species), and is more 

 modern in appearance, the frontal lobes being decidedjy broader, 

 and the convolutions richer and more sinuous. In the frontal 

 region the sulci tend to become less exactly transverse, and in 

 the parietal region a slight tendency to obliquity of the sulci is 

 observable. The olfactory lobes are large, and the cerebellum is 

 not overlapped by the hemispheres to the same degree as in the 

 recent species. 



IV. The Vertebral Column. 



1. Cervical Vertebra. The atlas (PI. XXII., Fig. 3) is rather 

 long antero-posteriorly in proportion to its breadth. The ante- 

 rior cotyli for the occipital condyles are deeply concave and are 

 notched, sometimes more and sometimes less deeply, on their 

 outer margins. Inferiorly they are almost in contact, but above 

 are widely separated by a deep and broad notch of semi-circular 

 outline. The neural arch is rather broad and low, and the neural 

 spine is represented by a low rugose ridge ; on each side of this 

 there is another similar ridge which runs obliquely forward and 

 outward, ending above the foramen for the first spinal nerve. 

 The inferior arch is strongly convex, and constricted in the 

 middle by the deep fossae into which the vertebrarterial canals 

 open ; there is a small but very distinct hypapophysial tubercle. 

 The posterior cotyli for the centrum of the axis are rather high 

 and narrow, and face obliquely backward and inward ; the artic- 

 ular surface for the odontoid process is in some cases separated 

 from the cotyli by deep grooves, either partially or completely ; 

 in others the two are continuous. The transverse processes are 

 very short, but extended from before backwards, with regularly 

 curved and slightly thickened free margins. When viewed from 

 the side, the process presents a slight sigmoid curvature, and 

 runs obliquely downward and backward. At the anterior root 

 of the transverse process there is a deep notch for the first 

 spinal nerve which is not converted into a foramen. The posterior 

 opening of the vertebrarterial canal is on the dorsal side of the 

 transverse process. In advance of its anterior opening there is 

 a small vascular opening, which enters but does not perforate 



