Page:Parasaurolophus walkeri, a new genus and species of trachodont dinosaur.pdf/15

Rh The appearance of the cross section is indicated in Figure 1, while Figure 2 is constructed to show the probable cross section of the crest when free from distortion. If this ﬁgure is correct the depth of the crest, 360 mm. from the end, is 130 mm., the superior diameter, 90 mm., and the inferior diameter, 85 mm.

In considering this remarkable structure, the question naturally arises as to the character of these hollow bones in life. Were they ﬁlled with organic tissues or were they open air passages? The external nares seem to lead directly into the upper pair of tubes, but nothing is known as to the internal nares. This interesting question could probably be answered by a longitudinal sawing through the skull, but we have been unwilling to injure the specimen so seriously.

Concerning the function of the crest itself, Brown is of the opinion that in Saurolophus it bore a frill and that this frill was probably continuous with a frill on the dorsal vertebral spines. There can be little doubt that a similar structure was present in Parasaurolophus, and we have reason to believe that a muscular or ligamental union existed between the crest and the dorsal vertebrae as will be more fully considered later.

Maxillary—This bone shows the ordinary well-marked sutures with the premaxillary and with the jugal: its relation to the lachrymal, however, is open to question. The actual suture with the premaxillary is 110 mm. long and with the lachrymal (?) 40 mm. long. There are 31 strongly carinated teeth visible in a length of 240 mm.

Lachrymal and prefrontal (Plate V, Fig. 2)—The identiﬁcation and relationship of these bones is extremely doubtful, but it is certain that this genus is remarkably different from any other trachodont in the arrangement of the bones of this part of the head. A detailed drawing (Plate V, Fig. 2) has been prepared of this part of the head to show the sutures as far as they can be made out. Posterior to the maxillary, and overlapping it, is a quadrangular to subtriangular bone which it seems necessary to interpret as a lachrymal. Its