The Ornithosauria / An elementary study of the bones of Pterodactyles made from fossil remains found in the Cambridge Upper Greensand, and arranged in the Woodwardian Museum of the University of Cambridge

by H. G. Seeley

The anterior zygapophysial processes are separated from the anterior articular surface of the centrum by a more or less oblique channel. Towards the base of this channel in many vertebræ may be seen a small and short flattened antero-posterior perforation corresponding in position with the usually large perforation for the vertebral artery. If the passages are to be regarded as having subserved such a function, it will not be without interest to remark the small relative size of the cerebellum in these animals; since the vertebral artery conveys the blood to that region of the brain.

The anterior zygapophyses are strong processes directed forward and outward, compressed a little from side to side; they are placed at the outer sides of the anterior articular face of the centrum, and extend in front of it.

The zygapophysial facet is commonly oval and looks upward and inward and forward.

The posterior zygapophyses are short and massive, but otherwise correspond closely with the anterior zygapophyses, only with all the parts reversed, and except that necessarily they are relatively to the neural canal a little higher.

A sharp and well defined angular ridge, commencing at the back of the zygapophysis, is directed inward, and forward, and upward along the posterior margin of the neural arch to the top of the neural spine. The posterior aspect of the neural arch is concave from side to side, and makes a right angle with the superior lateral aspect.

The part of the centrum exposed behind the neural arch is convex above from side to side.

The pneumatic foramen between the centrum and the neural arch varies greatly in size; it is oval and longitudinal.

The largest specimens have the centrum 2¹/₂ inches long; in the smallest the centrum measures ⁵/₈ths of an inch in length.

In the second type of cervical vertebra the side of the centrum makes a right angle with the base, and is separated from it by a sharp angle as in struthious birds. The side of the centrum is concave, with a few small pneumatic perforations; and the side of the centrum, which is high posteriorly, rounds over the oblique ridge connecting the zygapophyses, into the oblique lateral face of the neural arch. The anterior zygapophyses are very large and the posterior zygapophyses small and placed as high as the top of the neural canal.