288 BRiriSH FOSSIL REPTILES. 



With the foregoing knowledge of the complex structure of the sacrum of the 

 lu-uanodon, the peculiarities of detached parts of those modified vertebrae become 

 intelligible, and prove to be such as they were originally surmised to be.* 



Detached bodies of the Sacral Vertebra of the Iguanodon. PI. 12. Nat. size. 



As such parts, especially the centrum or body, are not unfrequently found 

 separated from the rest of the skeleton of immature individuals, it has appeared 

 desirable to subjoin a description of the most common of these parts. 



No. ^, Mantellian Collection, in the British Museum, is the centrum of a sacral 

 vertebra of a sub-quadrate form, with a broad and flattened inferior surface, PI. 12, 

 fig. 3, slightly concave lengthwise. The upper surface, fig. 4, is excavated by a wide and 

 moderately deep canal, indicating the unusual size, for Reptiles, of the sacral portion of 

 the spinal chord. The anterior, n, and posterior, »', parts of the sides of this centrum, 

 fig. 1, are raised, so as to form projecting sub-triangular rough articular surfaces, con- 

 tinued upon the margins of the neural canal, evidently for the attachment of the 

 neurapophyses and the heads of the strong sacral ribs. The interspace of these anterior 

 and posterior ncurapophysial surfaces is formed by a smooth oblique groove, o, figs. 1,4, 

 connecting the smooth surface of the spinal canal with that of the free lateral surface of 

 the vertebra, and indicating the place of exit of the sacral nerves : such outlet is neces- 

 sarily in this unusual situation, because the holes of conjugation, as they exist in other 

 vertebrae showing thp ordinary position of neural arches, have here been obliterated 

 by the impaction of the bases of the neurapophyses between the contiguous extremities 

 of the bodies of the sacral vertebrae. 



The anterior and posterior articular extremities of the present interesting fossil 

 equally bespeak the peculiar character of the sacral vertebrae of the Binosauria. They 

 are impressed by coarse straight ridges and grooves radiating from near the upper part 

 of the surface, fig. 2, like those on the corresponding part of a cetaceous vertebra when 

 the epiphysial articular extremity is removed. These inequalities are here, doubtless, 

 preparatory to that anchylosis by which the sacral vertebrte are compacted together in 

 the mature Dinosaurs. 



The length of this vertebral body . . , . 



The height . . • ■ . • 



The breadth of anterior articular end .... 



The breadth of middle part .... 



Antero-posterior diameter of anterior costal surface 



Antero-posterior diameter of posterior one 



* 'Report on Brit. Foss. Reptiles,' 1841, p. 130. 



