THE HORSE IN MOTION. 77 



same substance immediately enveloping the tendons. This under, or 

 proper, covering, however, is fibrous as well as cellular in composi- 

 tion. For the space of a hand's breadth below the knee the glistening 

 (tendinous) fibres may be seen crossing obliquely over the tendons, as 

 they run from the annular ligament of the knee to be implanted 

 into the external border of the cannon bone behind the external 

 splint bone. This forms the sheath of the tendons. And when we 

 slit it open we discover a cavity possessing a surface of a synovial 

 nature ; and a sac, or bursa, thereby formed, which extends half-way 

 down the leg, and is then closed. Through the bursa runs the per- 

 forans tendon, which may indeed be said to form a posterior boundary 

 to it. The interval between the flexor tendons and the suspensory 

 ligament, in their front, is likewise filled with interuniting cellular sub- 

 stance. This brief and imperfect anatomical sketch may serv^e to illus- 

 trate the nature of sprain. It will at once strike us that, although 

 the tendons themselves are incapable of extension, and are too firm 

 and strong in their texture to sustain hui't from any common accident, 

 yet that they are surrounded and connected together, as well as to the 

 parts contiguous to them, by a soft, delicate tissue which must, every 

 time they are forcibly pulled or stretched, be extremely liable to stretch 

 and lacerate ; and this, in fact, it is which in all ordinary cases consti- 

 tutes the true and sole nature of 'sprain of the back sinews.' " 



What is proved from the facts presented in the above quotation 

 is that laceration of the sheath of the tendons could not take place ex- 

 cept by the elongation of the tendon itself, and on that elasticity, or 

 spring, of these tendons, in conjunction with that of the suspensory 

 ligament proper, the mechanical action depends and in it their chief 

 value consists. 



The action of the anterior extremity as a unit in locomotion may 

 now be studied. As the limb is thrown forward and in the act of 

 taking the ground, it forms a straight line from the elbow to the heel ; 

 the toe is raised, as in the posterior extremity, and contact is made 

 with the heel. When the weight comes upon the foot the suspensory 

 ligament is put upon the stretch by the reflexion of the pastern. The 

 knee is kept in a straight position by the tension of the extensors. 



