86 PATAGONIAN EXPEDITIONS: PALEONTOLOGY. 



swollen, mamillate appearance, and is more extensively invaded by the 

 very large and conspicuous glenoid foramen : the zygomatic arch is shorter 

 and its dorsal border is continued as a low ridge up to the sagittal crest, 

 making a more definite posterior boundary to the temporal fossa. The 

 very large lachrymal is more extended upon the face and has no spine ; 

 the foramen is, as in DiadiapJwriis, placed in front of the orbit, not on its 

 rim, as it is in Proterotherium. The frontals are longer than in the latter, . 

 reaching farther behind the orbits, especially in the median line, where they 

 extend farther between the divergent ends of the parietals. The sinuses 

 are larger and cause more prominent protuberances on the forehead ; the 

 superficial prominence on each side is divided into two parts by the vas- 

 cular groove which runs forward from the supraorbital foramen. This 

 arrangement, which is not well shown in very young skulls, becomes very 

 conspicuous in old animals and gives a characteristic appearance to this 

 region of the skull. 



The nasals are considerably shorter than in Proterothermm^ longer than 

 in Diadiaphoriis and, as in the former, they articulate with the premaxillae, 

 though the suture is shorter. Consequently, the anterior nares are inter- 

 mediate in form between the two genera, being longer and more oblique 

 than in Proterothermm, shorter and more vertical than in Diadiaphorus. 

 Otherwise, the premaxillse are much as in Proterotherhmi^ but the incisive 

 foramina are larger and the spines correspondingly longer, and in the 

 edentulous region between the incisor and first premolar the palatal sur- 

 face is not so contracted, nor so distinctly demarcated from the lateral 

 surfaces. The facial, or preorbital, portion of the maxillary is lower dorso- 

 ventrally than in Proterotherium ; the palatine processes extend forward 

 between the premaxillae so as to take part in the formation of the incisive 

 foramina. The palate is of more uniform width than in the last named 

 genus and less deeply concave ; the palatines are very long. 



The mandible is very like that of Proterotherium, the differences being 

 chiefly in the ascending ramus, the ventral border of which descends less 

 below that of the horizontal ramus and thus the inferior profile of the jaw ! 



is less sinuous in this region ; the coronoid is more slender, recurved and 

 tapering, and the sigmoid notch is much wider, while the masseteric fossa ( 



is shallower. l 



Vertebral Cohimn and Ribs. — As already mentioned in the account of 

 the family given on a previous page (p. lo) the vertebral formula is quite 



