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PATAGONIAN EXPEDITIONS I PALAEONTOLOGY. 
and moderately curved, with convexity behind ; the proximal end is 
simple, without expansion or process, but on the posterior side, near the 
distal end, is a low, roughened ridge. No other hyoid element has yet 
been found. 
It is not practicable for me to make any detailed comparison between 
the skulls of Nesodon and Toxodon , for of the latter only a cast is at my 
Fig. 19. 
Nesodon conspurcatus ?: Skull, left side, X j. American Museum of Natural History. 
disposal, and in this cast but few of the sutures are shown. Nevertheless* 
instructive results may be obtained from a general comparison. The skull 
of Toxodon is manifestly of the same type as that of Nesodon , but has 
undergone considerable modification and exhibits many differences. The 
pre-orbital or facial region of the skull is somewhat longer in proportion to 
the cranial region than in the Santa Cruz genus. The occiput is much 
higher in relation to its width, and is more deeply and uniformly con- 
cave, with the lambdoid crest projecting prominently backward ; the fora- 
men magnum is less depressed and the occipital condyles are much more 
widely separated, especially ventrally. The auditory region is very differ- 
ent in being less specialized and more as in Pvotypotherimn than in Ne- 
sodon and more like the young skull than the adult of the latter genus, 
but in this respect there is considerable variation in the Pampean genus. 
