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An Account of a Peculiarity not hitherto described in the AnJele, 

 or Hock-joint of the Horse ; with Remarks on the Striicture 

 of the Vertebrce in the Species of Whale, entitled Delphinus 

 Diodon *. By Robert J. Graves, M. D., M. R. I. A., 

 King's Professor of the Institutes of Medicine, Honorary 

 Member of the Royal Medical Society of Berlin, of the Me- 

 dical Association of Hamburgh, &c. &c. 



j3eing engaged in the dissection of the horse, on examining 

 the hock-joint, I found that any effort to flex or bend the limb 

 at that joint, was counteracted by a considerable resistance, 

 which continued until the limb was bent to a certain extent ; 

 after which, suddenly and without the aid of any external force, 

 it attained to its extreme degree of flexion. In attempting to 

 restore the extended position of the limb, I found that a similar 

 impediment existed to its extension, until the same point was 

 passed, when the limb suddenly, as it were, snapped into its ex- 

 treme degree of extension at this joint. 



At first I conceived that this phenomenon depended on the 

 tendons of the flexor and extensor muscles of this joint ; but on 

 removing all these muscles and their tendons, it was not dimi- 

 nished, and it therefore became clear that it depended on some 

 peculiar mechanism within the joint itself. 



Before I enter into the details of this tnechanism, it is neces- 

 sary to remark, that it is evidently connected with the power this 

 animal possesses, of sleeping standing, for it serves the purpose 

 of keeping the hock-joint in the extended position, so far as to 

 counteract the oscillations of the body, without the aid of mus- 

 cular exertion ; and in this respect it resembles the provision 

 made to efifect a similar purpose in certain birds, as the stork, 

 and some others of the grallae, which sleep standing on one foot. 

 It will appear, also, in the sequel, that not only is the effect 

 produced the same, but the mechanism is in many respects si- 

 milar, if the account given by Cuvier, and also by Dr Ma- 

 cartney, in Rees* Cyclopaedia, article Birds, be correct. 



• Read 5tli July 1830, before "Royal Irish Academy, and just published in 

 the Memoirs. 



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