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FOSSIL REPTILIA OF THE 



cavities characteristic of the sacral vertebrse of the present genus ; in which I infer, from 

 the different relative expanse of the neural canal, as shown in the figures of the 

 vertebrae above compared, that the hind limbs were relatively less in Bothriospondylus 

 than in Iguanodon. They, probably, came nearer to Crocodilian proportions. 



A second more mutilated sacral centrum of Bothriospondylus (PI. IV, figs. 4, 5, 6) 

 shows the modification of that marked 4 in the sacrum of Ilylaosaurus, Tab. V, figs. 1 

 and 2, Monog. cit., in having the parapophysial expansion limited to one (j?) on each side 

 of the centrum. In the present genus its base occupies the anterior half of the lateral 

 surface, instead of the smaller proportion shown in Hylceosaurus ; it is also more 

 depressed, and the entire centrum is flatter, though not in so great a degree as in the 

 subject of PI. I above described. Both ends of the present centrum are flat, and show a 

 greater proportion .of the smooth unconfluent condition than in the subject of Plate III, 

 fig. 3. The supporting parts of the neural arch forming the roofs of each lateral cavity 

 (figs. 4 and 5,/) are broken off together with the arch itself, and but a small part of the 

 neural surface (ib., figs. 4 and 5, n) is preserved. 



This mutilation exposes the whole depth of the lateral excavations (fig. 4,/,/) of the 

 centrum, undermining, as it were, the base of the neural arch ; and these show that the 

 breadth of the centrum beneath that arch is reduced, about midway between the two 

 ends, a and 6 , to half an inch, the breadth of the centrum at the fore end, a , being, when 

 entire, 3 inches 3 lines. At the opposite or hinder end the breadth was less, and the 

 height apparently greater, whence it may be inferred that this vertebra was near to the 

 hinder end of the sacrum. 



The right half of the anterior, flat, smooth but irregularly indented, articular surface 

 of the centrum is nearly entire. Extending, as far as the origin of the pre-parapophysis, 

 p, which is preserved, and wanting only part of its upper surface, the entire transverse 

 extent can be estimated, as above noted. 



The under surface of the centrum (ib., fig. 6) is more convex across than in the 

 subject of fig. 1, PI. Ill, concomitantly with its greater extent in the present vertebra. 

 The longitudinal contour of the under surface (PI. IV, fig. 5) is more uniformly concave. 

 The margin of both articular ends is eroded. The aperture of the lateral excavation 

 (ib., fig. 4, c) is 1 inch 5 lines in longitudinal extent; but the cavity is continued 10 

 lines further above the pre-parapophysis (ib., jo) ; the depth of the excavation at the 

 middle of the vertebra is 1 inch 3 lines. The smooth compact crust of the centrum 

 passes, without fracture, over the free lateral tract (ib., fig. 5, c). The vertically convex 

 border of the floor of the cavity is somewhat thicker than in first-described sacral 

 vertebra, but similarly shows a natural condition and contour. The upper surface of the 

 floor of the cavity shows a fine crack (outside the letter / in fig. 4) as if the inner half of 

 that floor, with the adjoining part of the centrum {p) supporting the base of the neural 

 arch had been slightly depressed. 



