Page:Parasaurolophus walkeri, a new genus and species of trachodont dinosaur.pdf/20

16 spines increase in size as follows: 10th, 35 mm.; 11th, 40 mm.; 12th, 50 mm.; 13th, not measurable.

The ﬁrst measurable cervical rib is the ﬁfth which is long and slender, 105 mm. from diapophysis to tip. The sixth is shorter, and less pointed: its length is not measurable. The seventh to tenth inclusive are ﬂatter, broader, square at the end, and of about equal length–90 mm., 100 mm., 90 mm., 85 mm. The eleventh to thirteenth are more pointed. The eleventh is 90 mm. long and the thirteenth 120 mm. The twelfth is not well preserved.

The diapophyses of the cervical vertebrae are well developed: that of the axis is small and uncertain, that of the 7th vertebra is 60 mm. long.

The postzygopophyses are very strongly developed. From the eighth to the thirteenth they are curved down ward and carry a well-marked facette. The curvature of the postzygopophyses ceases abruptly with the ﬁrst dorsal. The lengths measured along the curve are approximately as follows: 3rd, 50 mm.; 5th, 70 mm.; 6th, 80 mm.; 8th, 85 mm.; 9th, 85 mm.; 10th, 90 mm.; 11th, 90 mm.; 12th, 100 mm; 13th, 110 mm.

Plate VII shows the eighth, ninth, and tenth cervical vertebrae from the left lateral, dorsal, and ventral points of view.

Dorsal vertebrae—There are apparently 17 dorsal vertebrae carrying ribs. The centra are decreasingly opisthocoelous posteriorly: the size of the centra is not measurable, but the posterior ones are approximately 80 mm. long, 150 mm. high, and 72 mm. wide.

The ﬁrst dorsal spine is distinctly more pointed than the last cervical, and the spines gradually increase in length posteriorly: they are rather variable in shape, and the posterior ones are closely set and both broad and long. The ﬁfth, sixth, and seventh show a remarkable modiﬁcation which will be referred to later.

The postzygopophysis of the ﬁrst dorsal is distinctly shorter than that of the last cervical, being only about 80 mm. long as compared with 110 mm, The second dorsal