306 PARTICULAR LAMENESSES. 



surface of an astragalus, the observer will see that the screw- 

 like motion is subject to three deviations. First, the dii-ection 

 is from within outwards for a short distance ; then it seems to 

 run perpendicularly ; and, finally, the lines of the prominences 

 are seen to curve towards the inner side and on to the inner 

 third of the cuneiform magnum, the inner prominence of tlie 

 asi-ragalus terminating abruptly, and leaving a hollow space 

 for the end of the internal prominence (malleolus) of the tibia. 

 This abrupt tennination allows the final act of flexion in the 

 hock to be performed with great velocity and suddenness. One 

 can see it in a fast-going, weU-actioned horse, giving sharpness 

 and grace to the hock action ; but whilst it allows this advantage,, 

 it is apt to be a so\irce of mischief, by acting directly upon the 

 cuneiform bones, and proving a source of concussion to them 

 during sharp flexion. This, in addition to the concussion 

 received when the foot comes to the ground, is sufficient to 

 cause inflammation of the cuneiform bones, end spavin. 



The relative obliquity and position of the true hock-joint,' 

 and the direction of its motion with relation to the production 

 of disease of the lower rows of bones, are subjects well worthy, 

 of consideration, and open a fair field of investigation to the 

 veterinaiy pathologist Pertinent to this matter, one might 

 naturally ask, V/hy should there be three rudimentary screws 

 on the surface of the astragalus ? The explanation is based' 

 upon the fact that the animal must be able to lock the joint 

 whilst asleep on its legs. It has been already explained that 

 the ligaments and the tendinous structure of the muscles of the^ 

 fore arm enable the fore legs to remain unbent during sleep.' 

 In addition to tendinous muscles and ligaments, we find that 

 the posterior extremities (and they are much more liable to 

 bend under the animal's weight, as may be witnessed in cases 

 of debility) are furnished v/ith a lock in the true hock -joint, — ■ 

 the lock being the deviation of the screw lines, which enables 

 it to sleep without falling. The remarkable manner in which 

 flexion of the true hock -joint is performed has been remarked 

 by Dr. Graves of Dublin; and a valuable paper by Professor 

 Dick on the subject, and on the conformation of the knee and 

 elbow joints, may be consvdted with advantage. It is printed 

 calong with his memoirs. 



Amongst the Taa-iety of hocks that a veteriuarj' surgecn 



