336 BRITISH FOSSIL REPTILES. 



Sandford, is in the Museum of the Geological Society ; and a portion of a third sacrum 

 from the Wealden formation, is in the British Museum. 



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

 their remarkable structure has w^ell repaid. 



It would seem that Cuvier did not regard the five anchylosed vertebrse, 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 ' Ossemcns Fossilcs,' and in 

 the description of the Plate (249, ed. iv, 1836), in which Dr. Buckland's figure is 

 reproduced as a " Suite de cinq vertcbres de Megalosaurus " (p. 23). In truth, the 

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

 two vertebrse, and therefore Dr. Buckland mentions this part in his original Memoir as 

 " five anchylosed joints of the vertebral column, including the two sacral and two 

 others, which are probably referable to the lumbar and caudal vertebr3e."t 



In contemplating this series of five anchylosed vertebrae, so new in Saurian 

 anatomy, at the period of preparing, in 1840, the 'Report on British Fossil Reptiles,' 

 for the British Association, my attention was first arrested by the singular position of 

 the foramina (PI. 25, /,/,/) for the transmission of the nerves from the inclosed spinal 

 marrow. These holes, which, in the plate illustrating Dr. Buckland's important 

 Memoir, are represented above the bodies of the three middle vertebrae, are natural 

 and are accurately given ; the smooth external surface 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 column in all 

 existing Saurians is at the interspace of two vertebrae, whence by French anatomists 

 these holes are termed "trous du conjugaison." In the sacrum of the Oxford Megalo- 

 saur, however, it is evident that above the anchylosed intervertebral space, i, a thick 

 and strong imperforate mass of bone, p, d, ascends to the neural platform, d, 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 composition and modifications of the vertebrae in the 

 different classes of Vertebrata soon enabled me to recognise the peculiar condition and 

 analogies of the five anchylosed vertebrae of the Megalosaurus ; with a view to illus- 

 trate which, I shall premise a few observations, on the different relative positions which 

 the peripheral vertebral elements may take, in regard to the central part or body. The 

 lateral vertebral elements, pleurapophyses, or " vertebral ribs," the inferior laminae or 

 haemapophyses, the superior laminae or neurapophyses, are all subject to such changes ; 

 but the neurapophyses are much more constant in their place of attachment than the 



* 'Transactions of the Geological Society,' 2d ser., vol. i, pi. 42. f lb., p. 395. 



