| Case. | Comp. | Tablet. | Specimen. |
| J | c | 2 | 1—43 |
Cervical Vertebræ.
[Pl. 9.]
Forty-three specimens are mounted to exemplify the variations in size and characters of cervical vertebræ. These for the most part are specific characters; and between the axis and the first dorsal vertebra the variations in an individual were slight. [Those nearest to the back, as in birds, are widest in front, and have the highest neural arches.] The associated series show commonly four cervical vertebræ behind the axis, and in two cases apparently five; never more. So that as seven appears to be the number of true cervical vertebræ in most if not all of the German Pterodactyles, it may be presumed that the Cretaceous Ornithosaurians also had this character in common, with Mammals, and probably as persistent. In Iguana there are 6, in Monitor 7, and in Crocodile 8.
The centrum is united to the neural arch as in birds, without a trace of suture; sometimes the neural arch is no wider than the centrum, sometimes it extends over the centrum on each side. Those forms with a narrow neural arch have the neural spine high, and its sides look forward as well as outward. The pneumatic foramen is oblique. An example is figured by Prof. Owen, in the memoir on Pterodactylus simus, pl. 2, fig. 4. The forms with a wide neural arch have the neural spine rising from the middle of the dorsal surface, erect and equally compressed from side to side. The pneumatic foramen is horizontal. An example is figured in Prof. Owen's memoir on Pt. simus, pl. 2, fig. 1. These two forms of cervical vertebræ may be regarded as typifying two genera.
In both forms many characters occur in common, and as the specimens illustrative of special modifications will be described hereafter, the following description has been made to embrace the chief characteristics of these vertebræ in Cretaceous Ornithosaurians.
The inferior aspect of the centrum is oblong (being narrower than long), or quadrate; when quadrate the additional lateral expansions are external to the pneumatic foramina, and are formed by the neural arch and zygapophyses. The centrum proper is a little wider in front than behind, and the side outlines are concave. The base of the centrum is flattened, or more or less hollow, or more or less tumid and regularly convex; in front there is often a mesial ridge, which never reaches the posterior articulation, and forms a prominent tubercle at the base of the anterior articulation. At the posterior end the outline of the centrum is concave, and mesially the bone has a hollow corresponding to the tubercle in front of the adjacent vertebra; and the part of the centrum on each side is prolonged slightly into a strong rounded or flattened tubercle below the side borders of the posterior articulation; these posterior processes, in vertebræ in situ, fitted, on each side of the mesial anterior process of the vertebra behind, on to concavities more or less marked. Analagous processes are developed in the cervical vertebræ of many birds.
All the Cretaceous Pterodactyles have the articular surfaces of the centrum transversely oblong, as have some birds. The posterior articulation is convex from side to side, and convex from above downward, and appears to extend a little further on this neural than on the hæmal surface; in outline it is commonly an elongated oval, but sometimes attends on the upper surface of the inferior lateral tubercles. The anterior articulation is transversely elongated, concave in both directions, and sub-triangular in outline; that is to say, the superior outline is more or less convex, and from its limits to the mesial tubercle at the base, the inferior outlines are more or less concave.
The neural canal is sub-circular or ovate in outline, and quite as large as the neural canal in vertebræ of Dinornis of similar size.
The neural arch like the centrum has commonly a depressed appearance. It always has a neural spinous process which is directed upward. In the depressed type the neural surface of the vertebra is in outline usually sub-quadrate, but concave at each side, and concave in front and behind; the four corners are the processes which support the zygapophysial facets, the surface is divided into two lateral parts by the strong neural spine. These lateral parts are from front to back flat, or slightly concave, or slightly convex; and from the neural spine outward they are always concave. The neural spine is commonly sharp in front and flattened behind. The neural arch is placed well forward, so that while a third of the neural canal remains uncovered by it behind, rarely a sixth would be uncovered in front.
The anterior and posterior zygapophyses are commonly connected by a more or less rounded ridge, undefined above, but well defined below, since under its posterior part at about the middle of the side of the centrum is placed the pneumatic foramen.