Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/104

18 "4. The head of the femur is set on at right angles to the shaft of the bone, so that the axis of the thigh-bone must have been parallel with the middle vertical plane of the body, as in birds.

"5. The posterior surface of the external condyle of the femur presents a strong crest, which passes between the head of the fibula and the tibia, as in birds. There is only a rudiment of this structure in other reptiles.

"6. The tibia has a great anterior or 'procnemial' crest, convex on the inner, and concave on the outer side. Nothing comparable to this exists in other reptiles; but a correspondingly developed crest exists in the great majority of birds, especially such as have great walking- or swimming-powers.

"7. The lower extremity of the fibula is much smaller than the other; it is, proportionally, a more slender bone than in other reptiles. In birds the distal end of the fibula thins away to a point, and it is a still more slender bone.

"8. Scelidosaurus has four complete toes, but there is a rudiment of a fifth metatarsal. The third, or middle, toe is the largest, and the metatarsal of the hallux is much smaller at its proximal than at its distal end. Iguanodon has three large toes, of which the middle is the longest. The slender proximal end of a first metatarsal has been found adherent to the inner face of the second, so that if the hallux was completely developed it was probably very small. No rudiment of the outer toe has been observed.

"It is clear, from the manner in which the three principal metatarsals articulate together, that they were very intimately and firmly united, and that a sufficient base for the support of the body was afforded by the spreading out of the phalangeal regions of the toes.

"From the great difference in size between the fore and hind limbs, Mantell and, more recently, Leidy have concluded that the Dinosauria (at least Iguanodon and Hadrosaurus) may have supported themselves for a longer or shorter period upon their hind legs. But the discovery made in the Weald by Mr. Beckles, of traces of large, three-toed foot-prints, of such a size and at such a distance apart that it is difficult to believe they can have been made by any thing but an Iguanodon, lead to the supposition that this vast reptile, and perhaps others of its family, must have walked, temporarily, or permanently, upon its hind legs.

"However this may be, there can be no doubt that the hind quarters of the Dinosauria wonderfully approached those of birds in their general structure, and, therefore, that these extinct reptiles were more closely allied to birds than any which now live".

There is one part of the organization of the Dinosauria which is not mentioned in this enunciation, because I did not at that time see its bearing upon the problem under discussion, I mean the very singular structure of the distal moiety of the tibia.

It took me a great deal of trouble to comprehend the structure of