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XI. On the mode of formation of the canal for containing the 
spinal marrow, and on the form of the fins ( if they deserve 
that name ) of the Proteosaurus. By Sir Everard Home, 
Bart. V.P.R.S. 
Read May 4th, 1820. 
T he last communication respecting the bones of the Proteo 
saurus which I laid before the Royal Society, contained so 
many important facts connected with the skeleton, that there 
was no room left to hope, I should ever again call the atten- 
tion of its members to this subject. 
Yet such has been the exertion made by some persons 
employed by Colonel Birch, to explore the cliffs at Lyme, in 
search of fossil organic remains, from an expectation that 
they will receive the full reward of their labours, that many 
new specimens have been lately collected ; in one of these 
which Colonel Birch has submitted to my observation, several 
bones are met with that have not been described, and which 
give a very important character to the vertebra*, and also form 
a more complete set of the bones of the fin. Of these I shall 
give a description, where their appearance is not sufficiently 
illustrated by the annexed Plate, (PI. XV.) 
Although the bodies of the vertebrae of this animal have 
been more frequently met with than any other bones, the 
manner in which the canal for the spinal marrow is formed, 
has not till now been made out. In this specimen we find 
