362 BRITISH FOSSIL REPTILES. 



an elliptical transverse section, and preserving the same breadth to their truncated 

 extremity : they extend outwards, and are slightly bent forwards : the breadtli of 

 this vertebra between the extremities of the transverse processes is 11 inches. The 

 neurapophysis is curved forwards from the base of the diapophysis to form the prezy- 

 gapophysis, or anterior oblique process : its length from the extremity of this process 

 to that of the posterior one is 3^ inches. The neurapophysis presents a simple convex 

 external surface up to the base of the neural spine ; the antero-posterior extent of this 

 process is 2 inches. The hsemal arches are from 4 to 5 inches in length near the base 

 of the tail (figs. 3 and 3*) ; they may be distinguished, like the diapophyses, by their 

 convex external surface ; their bases come into contact, as shown in fig. 3*, but are not 

 confluent as in the Iguanodon ; they articulate to two separate hypapophyses. 

 Between the pairs of these tubercles, which are placed at each end of the under 

 surface of the centrum, there is a longitudinal sulcus. The diapophyses soon lose the 

 slight anterior curve, stand straight out, decrease in length, and descend from the 

 neurapophysis to the centrum as the vertebrae approach the end of the tail. 



The haemal arches also decrease in length, but they expand in the antero-posterior 

 direction at their unattached and dependent extremity, which is defined by a slight 

 convex outline. Fig. 4 shows the modification of the under surface of the caudal 

 vertebroe, at the middle of the tail ; and fig. 5 gives a side view of one of the haemal 

 arches from this part, of the natural size. The following admeasurements give the 

 rate of decrease in length in the caudal vertebrae, taken at intervals of six joints : 



In. Lin. 

 Length of body of presumed 8th caudal . . . . .26 



Length of body of presumed 14th caudal . . . . .24 



Length of body of presumed 20th caudal . . . . .22 



The sides of the slender posterior vertebras are distinguished by a slight median 

 expansion below the base of the rudimental transverse process, so that the surface, 

 instead of being gently concave lengthwise, undulates by virtue of the middle elevation. 

 I have not met with this character in the corresponding vertebrae of other Saurians. 

 In the vertical direction the sides of the centrum in the posterior caudals converge at 

 almost a right angle to the inferior groove. The greater breadth of the centrum, in 

 proportion to its height, may still be discerned in the terminal caudal vertebrae (fig. 6): 

 thus in the centrum 2 inches 2 lines long, the breadth was 1 inch 10 lines, and the 

 height only 1 inch 3 lines. Here the bases of the short, but fore-and-aft extended, 

 haemapophyses appear to be confluent, as in fig. 7 ; but their peculiar shape would 

 serve to distinguish them from a haemal arch of an Iguanodon. 



* 'Keport on British Fossil Reptiles,' 1841, p. 114, 



