The distinctive aspect of these bones is given by the neural arch of the _axis_, which is very much elevated, and is formed by two flattened sides, which meet in a vertical ridge above the neural canal, and look forward, outward and upward; extending laterally more and more beyond the side of the centrum, but not reaching so far back as the posterior articulation of the centrum. Each side of the neural arch at its middle part behind is produced into a thick obliquely flattened process, the under portion of which shows the small posterior zygapophysial facets, which look downward, outward and backward. The lateral outline of the part of the neural arch above this process is concave; as is the lateral outline between it and the centrum. Behind, the neural arch is concave, and looks a little backward. The neural canal is stirrup-shaped in front, but is higher and sub-ovate behind. The neural arch of this, as of all the other vertebræ, except a few dorsals, is inseparably united to the centrum, without a trace of the line of union. In the middle of the side of the vertebra, and at what may be presumed to be the union between the neural arch and the centrum, in a concavity, is the pneumatic foramen. It is round or oval, and varies in form and size though not in position. In No. 8 it exhibits the subdivided reticular structure characteristic of the pneumatic foramina of birds. In No. 10, which has a short centrum, the pneumatic cavities are reduced to a few small perforations, no larger than would be made with fine needles. The centrum is shorter than in cervical vertebræ, commonly convex (No. 8) on the visceral surface; often with a slight longitudinal hypapophysial ridge (Nos. 1; 7; 12) rarely flattened (No. 10). Towards the hinder part the centrum widens, and becomes concave on the visceral surface, sending off as do the other cervicals, below the transversely elongated posterior articulation, a pair of short strong apophyses. The posterior articulation can only by a modification of the idea be said to conform to the cup-and-ball plan, for though convex from above downward and convex from side to side, the elongated transverse measurement would be three times the depth. On the under side an impressed transverse line divides the articulation from the concave part of the centrum below. Cervical Vertebræ. Pl. 9. Case. Comp. Tablet. Specimen. =J= _c_ 2 1-43