250 Prof. H. G. Seeley on the Ornithosaurian Pelvis. 



nearly 1| inch long, and is formed on the plan of that bone in 

 Pterodactylus longirostris. It is prolonged anteriorly as a 

 slender pointed rod f inch long, and posteriorly as a thick- 

 ened bar | inch long, which is truncated with a slightly 

 hamate downward curve. The depth to the inferior border of 

 the ischium is more than an inch. This border is straight. 

 The anterior pubic region is somewhat thickened, and its 

 ventral border meets that of the ischium at an angle, where 

 the thickened bone does not show either fracture or a definite 

 articular face. Below the ventral border lie two unsym- 

 metrical prepubic bones rather over an inch long and slightly 

 overlapping each other. I suppose these bones to have met 

 in the median ventral line. They are thin, expanded, slightly 

 curved, with a longitudinal ridge which separates a side which 

 is smooth from one which is granular. The thin plate is 

 imperfect in both bones, though the outlines are indicated. 

 This form of prepubis is quite distinct from that of the Ptero- 

 dactylce, and makes some approach to that of Rkampho- 

 rhynchus in its curved form. The terminal expansion of the 

 slender shaft or stalk of the bone is such as I have only seen 

 in association with an articular surface. 



In endeavouring to restore the pelvis it is necessary to 

 remember that there is no conclusive evidence of the relations 

 of the ischia to each other at their ventral approximation other 

 than evidence that they were not anchylosed together. It is 

 not certain that they were in close contact, though this is 

 probable, seeing that the prepubic bones certainly were anchy- 

 losed together in some species of Rhamphorhynchus ; and this 

 median union of the prepubic bones appears to have inclosed 

 a median pelvic vacuity which was usually heart-shaped or 

 kite-shaped, being wide in front and narrow behind. This 

 may be seen in the annexed restorations of the ventral aspect 

 of the pelvic bones, which I have made from models giving 

 the minimum approximation to the ischia (figs. 12, 13). 



It is probable that the pelvis was narrower in Dimorphodon 

 than this figure indicates ; but I see no reason to think that 

 the aspect of the fresh skeleton differed materially in these 

 genera from the restoration here given. The remarkable 

 structural feature shown is the ventral divergence of the 

 pubic bones from the median line of the body, the prolonga- 

 tion of the pubic arch to a median symphysis by means of the 

 prepubic bones, and the probable median union of the poste- 

 rior angles of the ischia. There is no evidence of the limit 

 to which pubic bones may be absorbed ; but if the prepubis 

 were to come to be attached in the region of the obturator 

 foramen, the bone would still be long enough to meet its 



