56 PATAGONIAN EXPEDITIONS: PALEONTOLOGY. 



and valleys of the inner side are better developed. The third milk-pre- 

 molar is the largest tooth of the temporary series, which is chiefly due to 

 the enlargement of the anterior crescent ; the antero-internal ridge is 

 smaller than in pg, but the postero-internal pillar is much more distinct. 

 The fourth temporary premolar is like p^^, except in being somewhat larger 

 and more completely molariform, as the antero-internal cusp is absent 

 and the posterior pillar larger. 



Sknli (Pis. VIII, figs. I, la, 4; IX, figs. 11, iia). — The skull is very 

 like that of DiadiapJwrns and LicapJiriitni, but has a lighter and more 

 graceful appearance, and there are many differences of detail. The 

 cranium is somewhat longer than in Diadiaphorits and the face corre- 

 spondingly shorter, but narrows forward more gradually. The orbit is 

 slightly lower in position and presents rather more directly outward. The 

 occiput is relatively broader and the foramen magnum lower and wider, 

 while the fossa between the exoccipital and the squamosal is narrower, so 

 that the periotic is nearly, and in some cases quite, excluded from the 

 surface of the skull. 



The parietal zone is somewhat longer and forms a slightly less full and 

 capacious brain-case, but extends a little farther down upon the side of 

 the cranium, narrowing the squamosals in a corresponding degree. The 

 zygomatic process is relatively broader dorso-ventrally and has a more 

 arched and elevated dorsal border, making a deeper groove between the 

 process and the side of the cranium ; the glenoid cavity is similar in form, 

 but has a deeper posterior concavity, and the postglenoid process is nar- 

 rower and less massive. Anteriorly, the zygomatic process extends farther 

 into the more deeply notched jugal. The orbit is closed behind, as in 

 DiadiapJwrus, but the posterior boundary, made up of the united frontal 

 and jugal processes, is more slender and less twisted : the lachrymal 

 foramen is larger and more conspicuous and has a more posterior position, 

 being placed on the rim of the orbit. The frontals are somewhat more 

 convex, which is probably due to a larger development of the sinuses. 



The most marked difference from the skull of Diadiaplwrits is to be 

 found in the nasals and premaxillaries. The nasals are much longer and 

 narrower and taper more gradually to the anterior point ; each is convex 

 transversely, so that there is a well marked depression along the median 

 line of suture between them : they have quite extensive sutures with the 

 premaxillaries, while in DiadiapJiorus there is no such contact. 



