38 THE SURGICAL ANATOMY OF THE HORSE 



The tendon of the superficial flexor of the digit is placed behind that 

 of the flexor perforans. This tendon in section is somewhat crescentic 

 in outline, its concave anterior surface embracing the posterior surface 

 of the perforans tendon. Near the middle line on the back of the 

 perforatus tendon is a small nerve. This is the branch of communication 

 between the internal and external plantar nerves. 



Plate XI. gives a representation of the appearance of a transverse 

 section taken across the fetlock. The saw has passed through the 

 large metacarpal bone immediately above its lower extremity, and 

 through the sesamoid bones just above their bases. The large meta- 

 carpal bone occupies the anterior half of the plate, and its outline is 

 approximately rectangular. In the middle line the anterior and posterior 

 borders present each a convexity. These indicate the positions where 

 the saw has passed through the antero-posterior articular ridge found on 

 the inferior extremity of this bone. 



On the anterior aspect of the large metacarpal bone two tendons are 

 seen : the one near the middle line is that of the extensor pedis muscle, 

 while the other is the tendon of the extensor suffraginis. 



Articulated to the posterior aspect of the large metacarpal are 

 the two sesamoid bones. Anteriorly each presents outwardly a large 

 slightly concave border where the bone is articulated to the convex area 

 on the large metacarpal, and inwardly another much less extensive 

 border, which is also slightly concave, and which is articulated to the 

 before-mentioned antero-posterior ridge. 



The outer border of the sesamoid bone is almost straight, and takes 

 a direction which is backwards and inwards. For the greater part this 

 border is subcutaneous, but between it and the skin anteriorly is the cor- 

 responding branch of the suspensory ligament which is passing round to 

 the front of the limb to join the tendon of the extensor pedis. Anteriorly 

 to this ligament the lateral ligament of the fetlock is severed near its 

 attachment to the large metacarpal bone. The postero-internal edge of 

 the sesamoid bone is slightly convex, and slopes backwards and outwards. 



