312 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 26, 



Mr. Abbay, the possessor of the magnificeiit left upper jaw of Mega- 

 losaurus now exhibited, to make a definite addition to our means of 

 reconstructing that monstrous Saurian. 



The jaw (Plate XII.) is 17'75 inches in length. At its anterior end 

 it measures 4-3 inches in a direction perpendicular to its length. Por 

 about an inch and a half from the anterior edge (a), which is entire and 

 shows the natural face of this part of the bone, the upper, or nasal, 

 margin is nearly parallel with the lower, or alveolar, margin; but further 

 back the bone was evidently produced into a great ascending process 

 (6), which divided the nasal from the orbital region. The base of 

 this process is fully four and a half inches long. Its anterior margin 

 slopes rapidly backwards and upwards, and seems to have been nearly 

 straight ; while the posterior margin is concave backwards and pre- 

 sents a natural edge, which formed the front boundary of the orbit. 

 The distance in a vertical line from the alveolar margin to the broken 

 upper extremity of the ascending process is 6*75 inches. Behind the 

 ascending process, the vertical diameter of the jaw diminishes, until, 

 at 10 inches from its anterior end, its vertical diameter does not ex- 

 ceed 2-Q in. Behind this point the jaw seems to diminish to a mere 

 bar of bone, not an inch deep at its posterior extremity. But the 

 impression on the lower part of the matrix which occupies the 

 cavity of the orbit shows that the natural edge of the jaw in this 

 region has been somewhat broken away, and that, if it were entire, 

 the depth of the jaw, at 12 inches from the anterior end, would be 

 2-1 inches, instead of only 1*7 inch as it appears to be. At this 

 place, namely 12 inches from the anterior end, the jaw is transversely 

 fractured ; and though the slender prolongation adjusts quite accu- 

 rately to the broken surface and e-vidently fitted on, it has, as evi- 

 dently, lost a good deal along its upper or orbital margin. 



Again, the general character of the slender posterior termination 

 of the jaw (c) is such that one would be inclined to think it could 

 not have been directly connected with any other bone; but the part 

 is so much injured that it is not safe to draw any very positive con- 

 clusions about the matter. The jaw is traversed by a vertical frac- 

 ture 2-4 inches from its anterior end. The fracture passes from the 

 alveolar margin to the nasal margin at the commencement of the 

 ascending process. I was at first disposed to think that the fracture 

 coincided with a suture between the praemaxilla and the maxilla ; but 

 closer examination does not confirm this supposition, the fracture 

 appearing to be altogether artificial. Hence it would appear either 

 that the praemaxilla and maxilla were so completely ankylosed that 

 all trace of their primitive separation is lost, or that the praemaxilla 

 has become detached from the maxilla, or that the jaw is simply the 

 praemaxilla — a possibility which must not be lost sight of in view of 

 the resemblances between Dinosauria and Birds. 



The teeth which remain in their places in the jaw, and are visible 

 from the outer side, are six in number. Five of these, the first, second, 

 third, fourth, and fifth, appear to be completely in place ; the third is 

 emerging. On the inner face of the jaw the crown of a sixth tooth, in 

 course of development, lies on the inner side of the base of the fifth. 



