Of the second type or genus No. 4 to 7 all show the anterior cup for the last lumbar vertebra. No. 3, 5 and 6 all show two entire vertebræ and part of a third preserved, but no specimen shows the posterior termination of the sacrum. No. 7 has the articular face of the centrum very broad, and greatly depressed. In No. 6 it is ovate and has the neural arch preserved; above a semicircular neural canal it sends out on each side a short horn-like zygapophysial process. No. 4 is remarkable for the small size of the circular neural canal, the centrum when entire measuring an inch from side to side, while the neural canal only measures 5/16 of an inch. No. 5 is figured by Prof. Owen. No. 4-6 appear to have given off transverse processes from the sides of the centra. No. 7 appears to widen into transverse processes at the point of suture between the centra.
In No. 3 the base of the sacrum is flattened, and its sides pinched in, and concave in outline from back to front. In this hollow are small pneumatic foramina, and between the hollows the vertebræ widen in the line of the suture so as to send out strong short transverse processes or tubercles. Above the hollows are given out the strong horizontal quadrate pyramidal transverse processes. All their sides are flattened or a little concave, and the under side displays a large ovate pneumatic foramen. Each of the four angles of the transverse process gives off a ridge. The lower ones descend obliquely to the anterior and posterior intersutural tubercles. The upper two ascend obliquely, in front and behind, and form rounded ridges on the neural spine. The neural spine is flattened, moderately compressed from side to side, and cupped a little over each transverse process. In front the neural spine is flattened transversely and perpendicular; the transverse processes are also flattened and a little in advance of the neural spine.
The sacrum in its general aspect is Mammalian. In the Bird the vertebræ are much more numerous and do not retain their individuality so well. In Reptiles properly so called, the sacrum never includes more than two or three vertebræ, and those commonly remain unanchylosed. But in almost any placental Mammal in which several vertebræ are anchylosed together, a sacrum similar to that of the Pterodactyle is met with. No mammalian sacrum, however, is furnished with pneumatic foramina.
| Case. | Comp. | Tablet. | Specimen. |
| J | c | 5 | 1—13 |
Caudal Vertebræ.
[Pl. 10.]
Thirteen specimens are mounted to exemplify the osteology of caudal vertebræ. No. 7 has been figured by Prof. Owen in the memoir on Pterodactylus simus, pl. 2 fig. 13-16. The centrum of the largest specimens measures one inch and a quarter long, and the vertebra is half an inch wide from side to side in the middle. The smallest specimen No. 13 has the centrum 3/4 of an inch long. The vertebræ vary in proportions, some being much more slender than others. They present a close approximation in form to the first type of cervical vertebræ, differing chiefly in being more elongated.
They are elongated bones constricted in the middle, so that the outlines of the sides seen from above or below are gently concave; the outline of the anterior end is sub-rhomboid, the outline of the posterior end is sub-pentagonal, as would be a transverse section of the vertebra. The long outlines of the base of the centrum and of the top of the neural arch are sub-parallel.
The two sides of the upper surface of the neural arch are smooth, flattened, a little concave from back to front; they are inclined to each other pent-house wise at about a right angle, and are separated throughout their length by a narrow slightly elevated neural spine. Behind, the neural arch is truncated transversely so as to expose the posterior neural surface of the centrum, which is convex from side to side. The outermost lateral angles of the neural arch are the posterior zygapophysial processes, short and strong above the centrum, with a tubercle on the upper surface, and showing the sub-circular zygapophysial facets behind; they look backward and downward, and are separated by a groove from the region of the centrum. Under the sharp ridge which connects these zygapophyses behind, the neural arch is excavated, and the cup shows the termination of three canals. The largest one is the upright oval of the neural canal in the middle, on each of its sides separated by a narrow bony wall is another perforation, very variable in size and shape, sometimes b& large as the neural canal, but usually small and circular. The anterior end of the neural arch is cut into, so that as seen from above, the straight sharp anterior margins diverge mesially from each other at a right angle, and so expose to view a small anterior part of the neural surface of the centrum. These lines are prolonged forward and outward, to form the upper margin of the anterior zygapophyses, which are compressed and prolonged over and beyond the sides of the anterior articulation, from which they are separated by a slight groove; the anterior and posterior zygapophyses are connected by a rounded ridge. The anterior end of the neural arch is excavated, but less so than the posterior end; in the middle is the oval perforation of the neural canal, and at the sides other perforations corresponding to those behind are placed a little in advance of the neural canal. The anterior and posterior articular surfaces differ in no respect from those of cervical vertebræ.
The inferior surface of the centrum is separated from the sides by two ridges parallel to the lateral concave outlines of the neural arch; they extend from sides of the front, more or less well marked, to the tubercular processes at the base of the sides of the centrum behind. The dice-box shaped area of the centrum so inscribed is usually concave from front to back, and concave from side to side behind, and convex from side to side in the middle; this convexity is only broken in front by the development of the slight mesial hypapophysial ridge.
The sides are narrow, flattened, look downward and outward, are a little concave from front to back, round into the centrum and into the neural arch, and show at about the middle a small pneumatic foramen, which is variable in size, but largest in No. 8, and sometimes a mere puncture.