ON BRITISH FOSSIL REPTILES. 105 



sis obliquely forwards to the under part of the transverse process ; behind 

 which ridge there is a deep depression, separating it from the posterior arti- 

 cular process. These processes are relatively smaller than in the Iguanodon, 

 and do not project beyond the hinder end of the centrum. The spinal plat- 

 form descends in a gentle curve from the posterior to the anterior oblique 

 processes : the base of the strong and thick spinous process follows this curve 

 along the middle line of the platform ; its antero-posterior extent was 4^ 

 inches, in a vertebra having the centrum of the same length, with a vertical 

 diameter of 4 inches, and measuring 7^ inches from the under part of the 

 centrum to the posterior part of the base of the spine. 



Sacrum. — The sacrum of the Megalosaurus consists of five anchylosed 

 vertebrae, and it is remarkable enough, considering how small a proportion 

 of the recognizable bones of this rare reptile has been found, that the present 

 characteristic part of the vertebral column of three different individuals should 

 have been obtained : one sacrum, from Stonesfield, is in the museum of Dr. 

 Buckland at Oxford ; a second sacrum, from Dry Sandford, in the museum of 

 the Geological Society ; and a third sacrum, from the Wealden formation, in 

 the British Museum. 



I have studied each of these specimens with much attention, which a recog- 

 nition of their remarkable structure has well repaid. 



It would seem that Cuvier did not regard the five anchylosed vertebrae 

 figured in Dr. Buckland's original memoir, as the sacrum of the Megalosaurus. 

 They are briefly alluded to in the second and fourth editions of the ' Osse- 

 mens Fossiles,' and in the description of the Plate, in which Dr. Buckland's 

 figure is reproduced as a ' Suite de cinq vertebres de Megalosaurus.' In truth 

 the sacrum was not known to be represented, at that time, in any Saurian by 

 more than two vertebrfe, and therefore Dr. Buckland mentions this part in 

 his original memoir as " five anchylosed joints of the vertebral column, in- 

 cluding the two sacral and two others, which are probably referable to the 

 lumbar and caudal vertebrae*." In contemplating this series of five anchy- 

 losed vertebrae, so new in Saurian anatomy, my attention was first arrested by 

 the singular position of the foramina for the transmission of the nerves from 

 the inclosed spinal marrow. These holes, which, in the plate illustrating Dr. 

 Buckland's important memoir f are represented above the bodies of the three 

 middle vertebrae, are natural, and accurately given : the smooth external sur- 

 face of the side of the vertebra may be traced continuing uninterruptedly 

 through these foramina, over the middle or nearly the middle of the centrum, 

 into the surface of the spinal canal. 



But the normal position of these foramina throughout the vertebral co- 

 lumn in all other reptiles is at the interspace of two vertebras, whence by 

 French anatomists these holes are termed ' trous du conjugaison.' In the 

 sacrum of the Oxford Megalosaur, however, it is evident that above the an- 

 chylosed intervertebral space a thick and strong imperforate mass of bone 

 ascends to the base of the spinous process, leaving it to be conjectured either 

 that the nerve had perforated the middle of the neurapophysis, or that these 

 vertebral elements had undergone in this region of the spine a change in their 

 usual relative position to the centrum. Previous researches into the compo- 

 sition and modifications of the vertebrae in the different classes of Vertebrata 

 soon enabled me to recognize the peculiar condition and analogies of the five an- 

 chylosed vertebrae of the Megalosaurus ; with a view to illustrate which I shall 

 premise a few observations on the different relative positions which the peri- 

 pheral vertebral elements may take in regard to the central part or body. 

 The lateral vertebral elements, or ribs, the inferior laminae or haemapophyses, 

 * Gcol. Trans., 2nd Series, vol. i. p. 395, pi. xlii. fig. I. t Ibid- 



