22 SCOTT. [Vol. V. 



fissura postica is longer than in the camel, and has a somewhat 

 less oblique position, running nearly parallel with the supra- 

 sylvian. Between these two sulci there is a short accessory 

 sulcus which runs from the hinder edge of the hemisphere, and 

 then curves downward to join the suprasylvian. The sylvian 

 fissure is quite long and nearly straight, and passes somewhat 

 obliquely upward and forward ; it appears to be both straighter 

 and longer than in the camel, especially the, pars posterior, which 

 in the camel is very short. The cast shows no indication of 

 a processus acimiinis. The rhinal sulcus is but very faintly 

 marked. 



The cerebellum is too much damaged in the two available 

 specimens for accurate description. It is relatively large, both 

 transversely and antero-posteriorly, and has a very broad, promi- 

 nent vermis, which rises from the medulla at nearly a right 

 angle, and when the skull is placed in a horizontal position, is 

 seen to project somewhat above the plane of the hemispheres. 

 The lateral lobes of the cerebellum are broader than the vermis, 

 and have high, nearly vertical, posterior faces. 



IV. The Vertebral Column (PL II, Figs. 1 1—^3). 



1. Cervical Vertebra;. — The atlas, as compared with that of 

 the recent Tylopoda, differs in some important respects, espe- 

 cially in its greater elongation in proportion to its transverse 

 breadth, and has a shape not altogether unlike that of Anoplo- 

 therimn. The anterior cotyli for the occipital condyles are 

 deeply concave and quite depressed ; inferiorly, they are almost 

 in contact in the median line ; superiorly, they are separated by 

 a deep emargination which is wider than in the existing tylopo- 

 dans. In the latter the external margin of each cotylus is 

 marked by a deep notch, which is but slightly indicated in 

 PoebrotJierium. The neural arch is higher, narrower, and more 

 convex than in the camel and llama, in which it is flattened, and 

 the neural spine is more distinctly indicated. The inferior arch 

 in the larger species, P. labiatum, resembles that of Auchenia in 

 having a strong median keel with a deep depression on each 

 side of it ; in the smaller P. Wilsoni, this appearance is less 

 distinct, and in th« camel the arch is regularly convex from side 

 to side. In the latter ffenus the anterior ed^e of the inferior 



