Vol. 69.] SKELETON OP ORN1THODESMUS LATIDENS, 375 



straight. There is no supra-occipital crest. The parietal region 

 is but slightly convex from side to side, and, compared with the 

 length of the skull, extremely constricted. 



There is no longitudinal arching of the cranial platform or the 

 occiput (PI. XXXVII, fig. 3). The crown and lateral borders of 

 the back of the skull are semicircular, and the base concave 

 (PL XXXVIII, fig. 1). The lower outer border is produced 

 posterior to the condyle. The intermediate area is deeply concave. 

 The brain-capsule is very small. 



I estimate the length of the skull to have been 560 mm., and 

 that of the mandibles 423 mm., which I obtain in the following 

 manner. From the angles at which the proximal and distal ends 

 of the humerus, radius, and ulna were lying on the blocks, the 

 missing section must have been about 89 mm. long. In the 

 measurements of the skull and limb-bones I have taken this to 

 be the length of the lost section. This would give the humerus 

 the same length as the British Museum specimen, which is 220 mm. 

 long ; and, as the preserved portions of that bone in the Atherfield 

 fossil are of the same size, it is no more than what would be 

 ■ expected. 



The Vacuities of the Skull. 



The External Xares. 



The external nares (PI. XXXVII, fig. 1, n.v.) begin not far from 

 the extremity of the snout. They gradually expand backwards 

 140 mm. Here should occur the missing section, and all further 

 trace of their shape and area would be lost, were it not for a moiety 

 of bone (PI. XXXVII, fig. 4, mx.n.b.) 50 mm. long and 18 mm. 

 deep, attached to the inner face of the maxilla, 236 mm. from the 

 end of the muzzle. This bone shows a thickening at its upper 

 interior edge. The lowest portion of the anterior border exhibits a 

 curved smooth outline, the extreme lower anterior boundary of the 

 antorbital vacuity, for I take this fragment of bone to be the lower 

 end of a maxillo-nasal process. It has on its upper extremity a 

 jagged fracture, thus proving a continuation of the bone in that 

 direction. Perhaps additional proof is added by the beak breaking 

 across, just posteriorly to this process, the weakest place in its 

 length. Again, if the narial opening was confluent with the 

 antorbital vacuity, the great cavity from the anterior border of the 

 nares to the anterior margin of the orbit, taken in conjunction 

 with the weak premaxillar bar and attenuated maxillae, would 

 appear to have been unable, without a strut, to prevent crumpling 

 on a strain of the jaws in prehension, for the weight of the skull 

 is distributed at both extremities. I believe that the rest of the 

 maxillo-nasal bar has been destroyed, and that the nasal was not 

 confluent with the antorbital vacuity. Granting this, the nasal 

 opening is enormous, subtriangular in shape, slightly oblique in 

 position, and posterior to the teeth. 



Q. J. G. S. No. 274. 2 c 



