282 Mr. H. G. Sccley on Omithopsis. 



He compares' the fossil to the tympanic bone of Mosa- 

 sauriis, with which it certainly has no near resemblance. In 

 the Palasontographical Society's volume for 1854 (Dinosam-ia, 

 part 2), Professor Owen figured a similar bone, which he 

 agreed with Dr. Mantell in regarding as tlie tympanic bone of 

 Iguanodon (p. 18), but suggests that it may possibly belong 

 to Cetiosaurus or Streptospondylus. This specimen I inter- 

 pret as the lower dorsal or lumbar vertebra of Ornithojms, 



Dr. Mantell's description is as follows : — 



" In these bones the body bears some resemblance to a ver- 

 tebra, but the large cells or hollows which pervade it through- 

 out readily distinguish it ; it forms a thick pillar or column, 

 which is contracted in the middle, and terminates at both ex- 

 tremities in an elliptical and nearly flat surface : two lateral 

 processes or alte pass off obliquely, and are small in proportion 

 to the size of the column. . . . From the great size of the body 

 in the fossil and the extreme thinness of its walls, the tym- 

 panic cellidffi must have been of considerable magnitude." 



In this description there is not one character which can 

 reasonably be presumed to characterize the quadrate bone of 

 Iguanodon^ or which is inconsistent with the identification of 

 the fossil as a lumbar vertebra ; for the cellular character, 

 which weighed with Dr. Mantell against making such a de- 

 termination, is seen, from the previous description of a cervical 

 vertebra, to be evidence in its favour. The following charac- 

 ters are shown in Professor Owen's or, rather, Mr. Dinkel's 

 figure. The centrum, from seven to eight inches long, shows 

 large internal air-cells and a dense outer film, like the speci- 

 men 28632. Posteriorly the articular surface is about four 

 inches deep, subcircular, and slightly hollowed. Anteriorly 

 the centrum seems to be larger; but the articular surface is not 

 preserved. The centrum is subcylindrical, expanded towards 

 both ends, so as externally to be concave from front to back 

 all round. 



The pneumatic foramen is placed towards the anterior end 

 of the vertebra, between the centrum and the neural arch. It 

 is from two to three inches in length, compressed behind, 

 about an inch high, and rounded in front. 



The lunate mass, in Prof. Owen's figure, above the pneu- 

 matic foramen, is the transverse process. It is an exceedingly 

 thin and dense film, only comparable to the transverse process 

 in similar vertebra; of birds. 



The affinities of this specimen are in accordance with the 

 avian type. If supposed to belong to an animal of like species 

 with the cervical vertebra, it would resemble Pterodactyles in the 

 smaller size of the back relatively to the neck ; in the elonga- 



