1 6 SCOTT. [Vol. V. 



zone hardly so long ; in the llama this zone is very much shorter 

 and the sagittal crest is reduced to very small limits. The 

 shape of the cranium in Anchenia is very different from that of 

 Pasbrotherium, being dome-shaped with its highest point at the 

 fronto-parietal suture, and the upper contour sloping downwards 

 and backwards to the occiput and anteriorly to the forehead, 

 while in PcebrotJierium and the camel the highest point is at the 

 crest of the inion, and from here the upper contour inclines 

 downward to the forehead. 



The squamosals are very large and form most of the side 

 walls of the cranium. The root of the zygomatic process is 

 less extended antero-posteriorly than in the llama, and the pro- 

 cess itself is rather shorter and straighter ; it is received ante- 

 riorly into a deep notch of the jugal. The glenoid cavity is 

 much extended from before backwards, and is nearly flat ; the 

 postglenoid is high and broad but very thin, and in close con- 

 tact with the bulla ; its articular surface is continuous with that 

 of the glenoid cavity, but in some specimens they are slightly 

 separated, while in the recent genera a wide and deep depres- 

 sion intervenes between the two. There is no elevation of the 

 outer margin of the glenoid cavity into a process, such as occurs 

 in the camel. The post-tympanic process of the squamosal is 

 short and closely united with the posterior lip of the meatus 

 auditorius. This process is placed much farther in advance of 

 the occipital condyles than in the existing species, and in conse- 

 quence the lambdoidal crest, when viewed from the side, has a 

 much more oblique course downward and forward. This elon- 

 gation of the posterior region of the cranium is common to the 

 primitive forms of many mammalian groups, and is brought 

 about, so far as we can judge, by the greater proportionate size 

 of the medulla oblongata and cerebellum. 



The jugal has a nearly straight course, running forward 

 nearly parallel with the axis of the skull and forming the lower 

 rim of the orbit in such a manner that it opens nearly straight 

 outwards and but little forward, though this eversion of the 

 posterior part is more strongly marked in the larger specimens 

 of P. labiatum. The postorbital process of the jugal is long, 

 slender, and curved, but does not quite reach the corresponding 

 process of the frontal, so that the orbit is not completely en- 

 closed by bone. The jugal extends further forward upon the 



