112 The Ottawa Naturalist [Dec. 



maxillae they send down a short, stout process to meet an ascend- 

 ing process from the premaxillae. This process is displaced 

 upward and forward on each side of the skull. The one on the 

 left side is seen, in the figure of the lateral aspect of the skull, 

 as a triangular projection silhouetted against the back part 

 of the nasal opening. In advance of the horn the nasals con- 

 tract rapidly and continue forward as a vertically narrow, 

 laterally compressed arch, which descends anteriorly in a sweep- 

 ing curve to join the premaxillae. A vertical nasal septum, 

 contributed to by each nasal, descends from their longitudinal 

 junction to form the upper margin of the nasal opening and in 

 front to join the premaxillae. This septum supplies to the 

 nasals anteriorly a large vertical surface of contact and greatly 

 strengthens them. An admirable provision for the support of 

 the nasal horn-core is seen in the formation of the nasal bones, 

 which, under the horn, form a massive, transverse arch, and 

 in front a longitudinal arch braced beneath by the septum, 

 the whole wonderfully adapted to withstand heavy strains trans- 

 mitted from the horn above. 



The maxilla narrows rapidly to the front, where it reaches 

 the premaxilla. Its upper half, which is overlapped behind by 

 the jugal, overhangs the lower half, whose concave hinder end 

 is covered by the triangular transverse bone. 



The premaxilla has a smooth surface, is narrow in front and 

 flares outward below. In lateral aspect it is obtusely angular 

 in front and beneath. It consists of a well defined marginal 

 strip of nearly the same breadth as, and in continuation down- 

 ward and backward of, the arched portion of the nasal, standing 

 out from and circumscribing below a sunken, inflected area, 

 which rises as a thin plate to meet the nasal septum anteriorly 

 and to form the lower free edge of the nasal opening behind. 

 It is overlapped at its front angle by the rostral bone, which fits 

 into a sutural groove between the premaxillae in front and is 

 closely applied to them as far back as the lower angulation. 

 Posteriorly an ascending process reaches the descending process 

 of the nasals. 



The exact boundaries between the frontals, prefrontals, 

 postfrontals and lachrymals have not been determined, as these 

 bones were coossified and the sutures between them are for the 

 most part obliterated. The frontals were not large and met 

 in the midline for a short distance only, as indicated seemingly 

 by impressed markings, which appear to be the remains of a 

 fronto-postfrontal suture. The postfrontals, however, were 

 extensively developed. In the midline anteriorly they met 

 for some distance in sutural contact, but posteriorly they were 

 widely separated by a long postfrontal fontanelle. They 



