Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/107

1869.] The determination of the true form of the distal end of the tibia of Megalosaurus had some interesting consequences.

In the 'Ossemens Fossiles' (éd. 4me, t. ix. p. 204, "Sauriens Fossiles"), the following passage occurs:—

"A lower portion of a tibia from Honfleur, with the astragalus, another bone of the tarsus, and a fragment which possibly belongs to the fibula indicate a hind foot of very extraordinary structure.

"To understand its nature, it is necessary to conceive that the leg to which these bones belonged was much compressed from side to side, so as to be sharp behind, like the tarsus of a duck, instead of being flattened from before backwards, like that of the Crocodiles, and still more that of the Monitors. Bearing this conception in mind, the bone a a, figs. 34–36, has some similarity in form to the astragalus of the Crocodile; but one sees that the calcaneum must have been altogether posterior and very small.

"The articular face of the tibia is 0⋅14 metre long; its greatest width (0⋅04) is towards its anterior fourth, which is acutely angulated; posteriorly, the inner edge is undulated. A curved crest ascends obliquely along the inner face of the tibia, and articulates with the ascending and compressed process of the astragalus. In consequence of its compression, the form of this astragalus is so curious that it might be taken, at first sight, for the calcaneum of a mammal.

"Below, it presents a convex cylindrical surface; above, it is irregularly concave, to adjust itself to the sinuosities of the articular face of the tibia; from its inner edge, posteriorly, arises the compressed process of which I have spoken. The internal face is semilunar. Behind, it is truncated, presenting a little concave facet, which undoubtedly articulated with the calcaneum.

"The animal to which this lower part of a leg and this tarsus belonged cannot have been less than thirty-six feet long, supposing it to have nearly the same proportions as the Gavials. If it had the proportions of a Monitor, its length must have amounted to forty-six feet."

Now, on comparing the distal end of the tibia of Megalosaurus with that of Cuvier's Honfleur Saurian, it was quite obvious that the two were closely analogous, and that Megalosaurus must have had an astragalus very like that of the Honfleur reptile. Evidence confirmatory of this conclusion was derived from another quarter.

The 'Mémoires de la Société Linnéenne de Normandie' (tome vi. 1838) contain a very remarkable paper by M. Eudes Deslongchamps, "Sur le Poikilopleuron Bucklandii, grand Saurien Fossile intermédiaire entre les Crocodiles et les Lézards," discovered in a Caen-stone quarry. The remains of this animal indicate that it had a length of from 25 to 30 feet; and as teeth of Megalosaurus Bucklandi occur in the Caen stone, Deslongchamps is inclined to suspect that Poikilopleuron may be identical with Megalosaurus. Among the bones of his Poikilopleuron, Deslongchamps obtained two astragali, the resemblance of which to the bone described by Cuvier in the 'Ossemens Fossiles,' was exceedingly striking ; and applying one of these bones to the end of a fragment which he had