432 MR. J. W. HULKE ON THE SKELETAL [NoV. 20, 



may be) lies in a deeper plane in the slab of rock, it is more distant 

 from the observer, as would naturally occur were the surfaces, and 

 not the median edges only, inclined towards each other. Taf. i. 

 fig. 2 , Taf. iv. fig. 5 show this point. This hint receives confirma- 

 tion from Zittel's very instructive plate of a specimen of Pterodac- 

 tylus suevicus from Nusplingen (42). In this is displayed the left 

 half of the pelvic girdle (seen in side view), shovring the three pelvic 

 bones still maintaining their normal relations, all contributing to form 

 the acetabulum. The ilium and ischium are apparently entire, but 

 the OS pubis, in form of a narrow bar, ends abruptly, as if by fracture, 

 at a short distance below the acetabulum. In front of the pubic 

 piece is seen a paddle-like or fan-like piece, which is obviously the 

 part regarded by some authors as prapubis. The close proximity 

 of this to the part denoted to be pubis by its relation to the aceta- 

 bulum and the correspondence of its stalk-like end to the apparently 

 fractured end of this suggest that the paddle-like piece originally 

 formed part of the pubic bone. The probabiHty of this view finds 

 strong confirmation in H. v. Meyer's figure of Pterodactylus micronyx 

 (op. cit. Taf iv. fig. 5), in which the two portions of the os 

 pubis, as I incline to regard them, are shown in their normal con- 

 nection, a slight apparent break of continuity in the pubic bar 

 marking the point where the paddle-like portion usually becomes 

 detached. Why should the separation of the two parts of the os 

 pubis so commonly occur at this point? The form of the pubis in 

 Bhamphorhynchus may elucidate this. The os pubis in this genus 

 has the form of a flattened bar bent angularly near its middle ; one 

 limb of it passes from the acetabulum downwards and forwards in an 

 approximately vertical plane, roughly parallel to that laid through 

 the median axial plane of the pelvis ; whilst the other limb, passing 

 transversely to this axis, meets the corresponding limb of the os pubis 

 of the other side, and unites with it in a median symphysis (42). 

 It is manifest that such an angular bend in the direction of its long 

 axis would be a weak point in the construction of the pubic bar, and 

 would favour its fracture at this point, under stresses acting in any 

 other direction than perpendicular to the plane whicli contains both 

 the limbs. 



In Dimorphodon, another genus, the evidence as yet available is 

 not opposed to the idea that its pubis is constructed on a similar 

 plan to that of Rhamphorhynchus, only the large foramen present 

 in this latter between the pubis and the ischium is in Dimorphodon 

 reduced to a narrow cleft. The larger of the two bones, marked 64 

 in R. Owen's figure of Dimorphodon, and identified by him as pubis 

 (praepubis), may with probability be regarded as the right pubis de- 

 tached from its normal connections and displaced, the left pubis 

 lying in advance of the ischium, from which it is separated by 

 a very narrow interval. 



If, then, in Ornithosauria the bone frequently termed the prae- 

 pubis is not such but only a detached part of a pubis of a common 

 Lacertilian plan, no corroboration can be found in it that the Croco- 

 dilian bone in question is a prsepubis. 



