BEOKEN KNEES. 481 



bone and fascia above tbe knee ; its use is to hold down the 

 extensor mefcacarpi, and to aid that muscle in extending the 

 limb. Surrounding the tendon a h (extensor metacarpi muscle), 

 is the sheath of the tendon, the inner surface of which (the 

 surface facing the tendon) secretes the necessary amount of 

 synovial fluid to lubricate the tendon. Of this synovial sheath 

 I shall have more to state presently. 



To complete the present description, I may mention that a 

 mass of fat is always situated between the back surface of the 

 tendon of the muscle a b, and the front of the synovial mem- 

 brane h, the uses of which are important. It aids in the 

 prevention of friction between the tendon a b and the mem- 

 brane k ; and also, in consequence of its acting as a pad to the 

 tendon, it will be a slight fulcrum to it, and give it a greater 

 directness of action when called into play. 



Now the structures most liable to injury, when a horse falls 

 with violence to the ground, are the skin, its sub-tissues, and 

 the tendon of the extensor metacarpi muscle (muscle ah c). It. 

 will be evident to the reader who reflects u,pon this matter, 

 that before the cavity of the knee (or, in other words, the joint of 

 the knee) can be exposed, the following structures must be 

 completely divided : 1st — The skin, which is always of great 

 thickness in front of the knee. 2nd — The fibrous tissue jj, 

 which is immediately behind the skin. 3rd — The synovial 

 sheath of the tendon of the extensor metacarpi. 4th — The 

 tendon of the extensor metacarpi muscle. 5th — -The fatty 

 substance behind the tendon ; and 6th — The synovial membrane 

 of the knee joint proper. 



The reader is not to understand, from the above, that the 

 knee joint proper never is exposed, because the contrary is the 

 fact ; but I am of opinion that the exposure of the joint is 

 far less common than is generally believed. - ■ 



2h 



