On the Osteology of Nvctosaurus. 139 



Owen* says that '■ the ribs of Dimorphodon acquire a characteristic 

 tenuity beyond the sixth pair," and Seeley mentions the fact that the 

 posterior ribs of the pterodactyls are slender. In current restorations of 

 the pterodactyls, the posterior ribs are often shown as long and strong 

 bones, inclosing a large and deep abdomen, the outlet of which must 

 have been through the narrow pelvis. It has been suspected that there 

 are sternal ribs intervening between the vertebral ribs and the sternum, 

 but there is no evidence of such in the present specimen. 



PECTORAL GIRDLE AND EXTREMITY. 



So far as is definitely known, the pectoral girdle comprises the ster- 

 num, coracoid and scapula only. No clavicles (unless the ossification 

 hereinafter described is a clavicle), inter-clavicle, epicoracoids, or precora- 

 coids, even, are known. Furthermore, the bones present are so strangely 

 modified that they present very little resemblance to the same elements 

 in other reptiles, agreeing rather better with those of birds, an agreement, 

 however, that I believe to be homoplastic in nature. 



Sternum. PI. XLII, Fig. 1. The sternum is a broad and thin bone, 

 with a stout anterior projection, and a thin, spatulate xiphisternal process 

 posteriorly. The presternal process is narrowed and rounded on the 

 under surface, and may have projected somewhat ventrad. The saddle- 

 shaped articular surfaces for the coracoids look dorsad and laterad. The 

 anterior borders at the sides of the presternal projection are thickened, 

 concave slightly in outline on the inner part, straight and more oblique 

 on the outer ends. The lateral margins are thin, and are nearly parallel 

 with the median axis of the bone. These borders have three emargina- 

 tions, separated by four rounded projections, the anterior one longer and 

 thicker than the others, which are thin and small. The posterior border 

 is convex on either side, ending in a short and deep concavity at each 

 side of the flat xiphisternal process. This process is spatulate, with the 

 distal end rounded or very slightly emarginate, and doubless gave attach- 

 ment to the series of abdominal ribs, which lie in the specimen nearly 

 in connection with it. The sternum is somewhat thickened in the middle 

 anteriorly, or back of the base of the anterior process. On the sides and 

 behind the bone is very thin, almost paper-like; this thinner part in the 

 specimen shows numerous small crinkly fractures, doubtless caused by the 

 flattening of the concave bone; similar crinkles are visible in the thin 

 prepubic bones. The sternum lies nearly in its normal position in the 

 skeleton. In falling backward it has been displaced a little obliquely to 

 the long axis of the body, as have the dorsal vertebrae, perhaps caused by 



* Paleontographica Soc, 1869, p. 69. 



