Page:Parasaurolophus walkeri, a new genus and species of trachodont dinosaur.pdf/19

Rh the inferior point of the suture between the surangular and dentary to the posterior tip of the articular is 115 mm. The strong flexure of the neck and the displacement of the anterior vertebrae have revealed the foramen magnum, which is small and apparently low in position. The other features of the posterior aspect of the skull are not well shown, but present nothing differing from the usual trachodont arrangement.

The vertebral column consists of 13 cervicals, 17 dorsals, 7 sacrals, and 6 caudals preserved. The vertebrae of the sacral region are not sufﬁciently exposed in the mount to state deﬁnitely how many are coalesced. The actual conditions are shown in the photograph (Plate VI). It is apparent that the vertebral centra shown in Plate I are very largely restored.

Cervicals (Plate VII, Figs. 1, 2, 3)—The total length of the thirteen cervicals measured along the line of the diapophyses is about 1190 mm. A more accurate measurement is 670 mm. along the ventral side from the posterior rim of the 7th to the posterior rim of the 13th vertebra. The cervical centra are strongly opisthocoelous. Cervical ribs are present, but owing to the neck having been forced between the mandibles the anterior cervical ribs do not appear. The most striking feature of the neck is the remarkably strong and prominent postzygopophyses.

The atlas is not well exposed: the length of the neural arch is 70 mm. and the maximum diameter across the two arches is 110 mm.

The axis carries the usual prominent plate-like neural spine, which is 85 mm. long on the midline. The total length to the posterior point of the postzygopophysis is 14.5 mm., and the width between the external surfaces of the two zygopophyses is 80 mm. The postzygopophysial facette is 38 mm. long.

The ﬁrst apparent neural spine after that of the axis is the ninth, which is only about 10 mm. high. Posteriorly the