272 PALEONTOLOGY. 



coracoid are long and narrow, but strong. The breast-bone 

 had a short but strong and deep keel, continued forward, in 

 advance of the cavities for the coracoids much further than 

 in birds ; and the body of the bone expands into a semicircular, 

 slightly convex, disc, separated by a constriction from the 

 narrower keeled part, supporting the coracoids. The vertebrae 

 of the neck are few compared with those of birds ; but they 

 are large and strong, for the support of a large head with long 

 jaws, armed with sharp-pointed teeth. The skull is, however, 

 lightened by large vacuities, of which one (p, fig. 97) is inter- 

 posed between the nostril n and the orbit I. The vertebrae of 

 the back are small, and grow less to the tail. They are more 

 numerous than in birds, there being in some species seventeen, 

 including one or two ribless or lumbar vertebrae. Those of 

 the sacrum are small, from three to seven in number : but 

 the pelvis is weak, and the hind limbs bespeak a creature 

 unable to stand and walk like a bird. The body must have 

 been dragged along the ground like that of a bat. The 

 Pterosauria may have been good swimmers as well as flyers. 

 The wings were outstretched membranes, as in bats ; the skin 

 of the body was apparently smooth, or finely wrinkled ; no 

 trace at least of scales, hairs, or feathers, has been manifested in 

 the fine-grained stone (lithographic), most rich in Pterodactyle 

 remains ; and in which the fine " bone-tendons," and delicate 

 sclerotic plates of the eye are preserved. The A r ertebral bodies 

 unite by ball-and-socket joints, the cup being anterior, and in 

 them we have the earliest manifestation of the " proccelian " 

 type of vertebra. The atlas consists of a discoid centrum, 

 and of two slender neurapophyses ; the centrum of the axis 

 is ten times longer than that of the atlas, with which it ulti- 

 mately coalesces ; it sends off from its under and back part a 

 pair of processes, above which is the transversely extended 

 convexity articulating with the third cervical vertebra. In 

 each vertebra there is a large pneumatic foramen at the middle 



