28 PROCEEDINGS OF THE GEOLOGICAL society. __| Nov. 10, 
Thus the ischia of a Dinosaurian are more bird-like than those of 
any existing reptile, but retain the reptilian union in a symphysis. 
3. Inall reptiles the pubis is inclined forwards as well as down- 
wards towards the ventral median line. In all except the Crocodile 
it takes a considerable share in the formation of the acetabulum ; 
and in all, except the Crocodile again,-the ossified pubis unites 
directly with its fellow in the middle line. In the Crocodiles, the 
inner extremities of the pubes remain cartilaginous for a great ex- 
tent, and consequently the ossified parts of the pubes remain widely 
apart in the dry skeleton. 
Prof. Phillips has shown me what I believe to be fragments of the 
pubes of Megalosaurus in the Oxford Museum. If the determina- 
tion is correct, they resembled those of the Ostrich in many re- 
spects. As they are detached, there is no certainty respecting their 
direction. The pubes of Compsognathus are, unfortunately, obscured 
by the femora. They seem to have been very slender; and they 
are directed forwards and downwards, like those of lizards. Some 
lizards, in fact, have pubes which, if the animal were fossilized in 
the same position as Compsognathus, would be very similar in form 
and direction. 
Hypsilophodon, however, affords unequivocal evidences of a fur- 
ther step towards the bird. The pubes are not only as slender and 
elongated as in the most typical bird, but they are directed down- 
wards and backwards parallel with the ischia, thus leaving only a 
very narrow and elongated obturator foramen, which is divided 
by the obturator process. I suspect that if only the pubis and the 
ischium of Hypsilophodon had been discovered, they would have 
been unhesitatingly referred to Aves. 
Thus, as far as its pubis is concerned, Hypsilophodon affords an 
unmistakable transition between Reptilia and Aves. It remains to 
be seen how far the hypsilophodont modification extended among the 
Dinosauria. The remains of Compsognathus and of Stenopelya lead 
me to suppose that it was by no means universal. In fact in this, 
as In many other respects, I have reason to think that the Dino- 
sauria present us with serial modifications leading from the Para- 
suchian* type of structure, on the one hand, to that of Birds on the 
other. 
The evidence yielded by the distal end of the tibia and the astra- 
galus has the same tendency. 
In the splendid collection of Megalosaurian remains in the pos- 
session of Mr, James Parker, of Oxford, which I had the good 
fortune to see a few weeks ago, I recognized the astragalus of that 
reptile, which, as I had already divined from the structure of the 
tibia, is altogether ike the corresponding bone in Povkilopleuron. 
In another specimen the distal end of the tibia and the fibula 
were in place, and there was the impression of the ascending pro- 
cess of the astragalus, with a fragment of ity bony substance, ex- 
actly where it should be. With this complete knowledge of the 
* By the generic name Parasuchus I indicate a reptile from the Indian 
Trias, which I hope shortly to describe, and which is clearly allied to Belodon. 
