9 



89 



diodon, by Dr. Jacob, were captured near Dublin, one of which, 

 measuring about sixteen feet in length, I procured for the purpose 

 of preparing its skeleton. 



After the spinal column had undergone maceration for a few 

 days, I found that the intervertebral substance could be easily de- 

 tached from the bodies of the vertebrae, and that it carried with it, 

 firmly attached to each of its extremities, a flat circular bone, 

 about a quarter of an inch in thickness, and exactly corresponding in 

 the extent and shape of its surface, to the surface of the body of the 

 vertebra, from which it had been separated. 



The separation was effected with facility, and took place sponta- 

 neously and completely when the maceration had been continued 

 some time longer. 



The surface of the flat bone, where it had been adherent to the 

 body of the vertebra, was of a spongy texture, afforded a passage to 

 many blood-vessels, and was marked by numerous sharp projections 

 and deep furrows, diverging from its centre, and answering to simi- 

 lar projections and furrows on the denuded extremity of the vertebra ; 

 of course the surface of these bones varied in shape and size with the 

 extremities of the vertebrae to which they were attached, being from 

 five to six inches in diameter at the dorsal, and not more than one 

 inch at the last caudal vertebra. 



The substance of these bones towards the intervertebral substance 

 was of much harder and closer texture than that of the bodies of the 

 vertebrae themselves, and where it was adherent to the intervertebral 

 substance, it had a smooth surface, marked with a great number of 

 concentric lines, answering to the arrangement of the fibres in the 

 intervertebral tissue, which adhered to this face of the bone with 

 great strength. This marking was deficient towards the centre where 

 the intervertebral substance is fluid. 



The facility with which these bones are detached, is the reason 



