Page:Parasaurolophus walkeri, a new genus and species of trachodont dinosaur.pdf/16

12 suture with the jugal is distinct and it is separated from the nasal (premaxillary?) by a deep pit which extends forward above the maxillary and backward between the nasal and the frontal almost to the end of the crest. Supero—posteriorly there is a distinct suture with the bone behind, but infero-posteriorly there is more doubt. While it can not be stated with certainty there seems to be a small triangular bone separating the infero-posterior margin of the lachrymal from the jugal: this bone we are inclined to regard as the prefrontal.

If the interpretation above is correct the lachrymal in Parasaurolophus is unique among the dinosaurs: in no other case is it so far forward or is it excluded from the orbital rim.

The distinctness of the little bone which we have called the prefrontal is very doubtful; it may be merely a process of the jugal, as the occurrence of a suture along its inferior border is open to question. As in the case of the lachrymal the exclusion of the prefrontal from the orbital rim is remarkable.

If this little bone is a mere process of the jugal, the anterior part of the bone to be described later as the frontal may be the prefrontal. No suture is visible above the orbit, but the bone in this region is in a poor state of preservation, and the absence of a suture cannot he stated with certainty. This interpretation will doubtless appeal to many anatomists, as it leaves the prefrontal, at least, in the normal position above the orbit and forming part of the orbital rim.

Frontal—This bone is unusually conspicuous as it forms the whole of the lower half of the crest, and, apparently at least, the whole of the supraorbital rim. As already stated, however, the anterior part of this bone may possibly represent the prefrontal. The suture with the postfrontal is distinct and as indicated in the drawing.

Postfrontal—This bone is normal in character and position: its sutures with the frontal and with the squamosal are distinct.

Jugal—This bone is of normal type: it is apparently not in contact with the quadrate, but as the superior point of