690 Bulletin American Museum of Natural History. [Vol. XIX, 



quadrate is flattened on its ventral aspect and somewhat cylin- 

 drically concave on its dorsal surface. The head is elongated 

 transversely to a length of 147 mm., the facet which articu- 

 lates with the lower jaw being somewhat saddle-shaped. 

 The posterior end of the quadrate is embraced between the 

 exoccipital and the squamosal bones. The qnadratopigals are 

 comparatively small bones lying between the quadrates and 

 the jugals. Dorsally they extend in thin, plate-like expan- 

 sions between the aforesaid bones, and in their posterior por- 

 tions form part of the infratemporal arcade, almost, if not 

 quite, meeting the forwardly extending process of the squa- 

 mosals. In their ventral portion where the distance widens 

 between the quadrates and the jugals the quadratojugals 

 dilate into a thick, wedge-shaped mass to fill the gap. The 

 greatest thickness is 89 mm. 



The occipital region of the skull is rendered very massive to 

 support the great weight of the head, the sutures between 

 the various elements being closed. The occipital condyle is 

 almost spherical, and has a diameter of 115 mm. It looks 

 almost directly backward and but little downward. ■ An- 

 teriorly it merges into a heavy basioccipital and laterally into 

 the exoccipitals, the limits of these three elements in the 

 condyle itself not being discernible. 



The basioccipital diverges into two stout limbs with heavy, 

 rugose extremities, in front of which appear the pulley -like 

 basisphenoid bones, the parasphenoid (" vomer ') arising be- 

 tween the limbs. 



The exoccipitals run out laterally to join the quadrates and 

 squamosals, overlapping the former and firmly articulating 

 with the latter to afford a strong brace across the entire base 

 of the frill. They thin away posteriorly and are, together with 

 the supraoccipital, overlain b}^ the largely developed parietals 

 which form the median element of the frill. 



The ventral aspect of the frill or crest is well shown in 

 Plate LIX, and is without vacuities of any sort, although 

 just behind the exoccipital bones the parietals are excessively 

 thin. Vascular impressions occur on the posterior half of the 

 parietal bones on either side, but there is no evidence of a 



