62 Dr Graves on the Struchire of 



culating surfaces, a sudden motion of flexion or extension is 

 thus produced. 



The preceding explanation supposes the ligaments of this 

 joint to possess, contrary to the nature of hgaments in general, 

 a certain degree of elasticity, which was evidently the case in 

 all, but particularly in the most deep-seated of those on the in- 

 ner side of the joint, which, therefore, appears most concerned 

 in producing the sudden motion, whether of flexion or exten- 

 sion. 



In the autumn of 1 8f?9, two of the species of whale called 

 Delphinus diodon, by Hunter, Hyperoodon, by La-Cepede, and 

 Cetodiodon, 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 

 detached 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 cor- 

 responding in the extent and shape of its surface, to the sur- 

 face of the body of the vertebra, from which it had been sepa- 

 rated. 



The separation was effected with facility, and took place 

 spontaneously 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 bloodvessels, and was marked by numerous 

 sharp projections and deep furrows, diverging from its centre, 

 and answering to similar 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 dia- 

 meter at the dorsal, and not more than one inch at the last cau- 

 dal vertebra. 



The substance of these bones towards the intervertebral sub- 

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

 bodies of the vertebrae themselves, and where it was adherent to 



