20 PATAGONIAN EXPEDITIONS: PALAEONTOLOGY. 



fraorbital canal is very short and has a much more anterior position than 

 in the recent genus ; posteriorly it is continued as an open groove, which 

 is not indicated in the latter. In correlation with the extreme reduction 

 of the teeth, the alveolar process is quite insignificant, but its edentulous 

 portion is extended forward for the whole length of the maxillary, as a 

 delicate though distinct ridge, which sharply demarcates the palatal from 

 the facial surface. The very long palatine processes are widest between 

 the teeth, narrowing somewhat behind them and still more, though very 

 gradually, in front of them. As a whole, the maxillary portion of the 

 palate is slightly concave transversely, but each palatine process is convex 

 in the same direction, which is produced by a deep median groove, with 

 a low ridge along the line of suture. Groove and ridge are much more 

 distinct in one of the specimens than in the other and are not apparent in 

 Tatu. 



The palatines are quite large and form a considerable extent of the hard 

 palate ; their external borders, as in the maxillary region, are thin ridges, 

 which distinguish the lateral from the palatal surface ; these ridges con- 

 verge posteriorly, where the infero-lateral surface of the palatines becomes 

 quite broad, and are continued over upon the pterygoids. Unfortunately, 

 the shape of the posterior nares cannot be clearly made out in either speci- 

 men, as the edges are broken ; it is apparent, however, that the opening is 

 much longer and narrower and extends farther forward between the pala- 

 tines than in Tatu. 



The pterygoids are small bones, mostly concealed from view by the pos- 

 terior extension of the palatines. Hamular processes and fossae are absent, 

 but the free border is broadened and thickened, though without the swollen 

 appearance seen in Tatu; this border forms an angulation between the 

 ventral and posterior sides, such as does not occur in the modern genus. 



The vomer, which is very long and narrow, is not visible in the pos- 

 terior nares, but extends along the ventral side of the mesethmoid. The 

 latter is very extensively ossified, forming a complete nasal septum, with 

 thickened dorsal and ventral borders. Beneath the cribriform plate it curves 

 downward behind the vomer and unites with the palatines. 



The cranial foramina are quite characteristic. High up in the orbit is a 

 long vertical slit, which encloses two separate foramina ; of these, the upper 

 one is the optic foramen and the lower one is the foramen lacerum ante- 

 rius. In the same vertical line with the latter, but well below it, is the 



