1917] 



Stock: Skull a)id Dentition of Nothrotherium 



115 



Gravigrada, the front margin being a little behind - . . ."- :t The 

 pterygoid plates continue backward from the shelf, formed by palatine 

 and in part also by maxillary, along either side of the postpalatine 

 notch. On these plates the inferior border is broadly rounded while in 

 Megatherium it is angnlate. In the Rancho La Brea Nothrotherium 

 the plates are very similar to those in Bernhardt 's specimen, and pos- 

 teriorly are seen to enlarge into great bullae as in the latter form. 

 These bullae differ decidedly from those shown by Reinhardt in being 

 pierced along their inner ventral wall by a large and elongate orifice. 

 Between the outer border of this opening and the inferior border of 

 the pterygoid plate a broad groove extends from the outer posterior 

 to the inner anterior side, diagonally across the inflated portion. The 

 posterior border of the pterygoid may approach the occipital condyles 

 very closely, thus differing decidedly from Megalonyx. 



The inflated pterygoids are perfectly preserved in skull 208 (fig. 3) 

 in which specimen they swell outward somewhat below the base of the 

 zygoma and behind the glenoid fossa. They are much better preserved 

 than in the skull, no. 15, originally described. In an earlier note on 

 the skull of the Rancho La Brea Nothrotherium the writer inadvert- 

 ently referred to these structures as tympanic bullae, stating that 

 Reinhardt considered them as such in the Brazilian species. In this 

 respect unfortunately Reinhardt has been misquoted, as he distinctly 

 and correctly interprets them as being merely inflations of the posterior 

 portions of the pterygoid. The pterygoid bullae in all the skulls except 

 one are large. In no. 313, which is the smallest of the eight nearly 

 complete skulls contained in the Museum of History, Science and Art 

 of Los Angeles, and evidently belongs to a somewhat younger indi- 

 vidual, the posterior inflation of the pterygoid is exceedingly small 

 and is restricted to the extreme posterior end of the pterygoid. The 

 ventral opening of the bulla is also small. Between the cavity and 

 the descending plate, the pterygoid is thickened in this specimen. 



In Hapalops longiceps, according to Scott, "The pterygoids are 

 narrow, inconspicuous plates, closely applied to the descending pro- 

 cesses of the alisphenoids, and not in the least like the swollen, bulla- 

 like bones of Nothrotherium, which Reinhardt has described ( '78, 

 336). " 24 Structures comparable to the pterygoid bullae of Noth- 

 rotherium and occupying a similar position are absent in Megalonyx. 

 Lindahl, however, records that in M. leidyi, "capacious air sinuses 



23 Scott, W. B., op. cit., p. 326, 1904. 

 2-4 Scott, W. B., op. cit., p. 185, 1903. 



