An account of a Peculiarity not hitherto described in the Ankle, or 

 Hock-joint of the Home ; with Remarks on the Structure of the 

 Vertebra 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 Medi- 

 cal Society of Berlin, of the Medical Association of Hamburgh, 

 SfC. ^c. 



Read July 5th, 1830. 



Being 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 exten- 

 sion, until the same point was passed, when the limb suddenly, as it 

 were, snapped into its extreme degree of extension at this joint. 



At first I conceived that this phenomenon depended on the ten- 

 dons of the flexor and extensor muscles of this joint; but on removing 

 all these muscles and their tendons, it was not diminished, and it 

 therefore became clear that it depended on some peculiar mechanism 

 within the joint itself. 



Before I enter into the details of this mechanism, it is necessary 

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

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



VOL. XVI. O 



