MUSCULAR SYSTEM. 145 



vial sheath, formed principally by the tendo perforatus ; from 

 which it only emerges at the division of the latter. Opposite 

 to the OS coronae it is destitute of any tendinous covering, and 

 is invested by cellular membrane only. It next sinks into the 

 substance of the frog, passing over the navicular bone, where 

 it becomes cartilaginous, and adapted in shape to the posterior 

 articular surface of that bone, a bursa or circumscribed syno- 

 vial cavity existing between them. Finally, it ends in an ex- 

 panded termination which is broadly implanted into the posterior 

 concavity of the os pedis. 



Action, — To bend the foot. It will also assist in the flexion 

 of the pastern, fetlock, and leg. 



RADiALis ACCESsoRius. — Flcxof uccessorius. 



Situation. — Deep-seated, along the infero-posterior side of the 

 arm. 



Figure. — Irregular; short; flattened : upper part, bifurcate. 



Attachment. — Superiorly, mesio-posterior part of the radius : 

 inferiorly, its tendon joins that of the perforans. 



Relations. — Anteriorly, with the radius ; posteriorly, with the 

 bellies of the perforatus and perforans : internally, with the radial 

 blood vessels and nerves. 



Direction. — From above downwards, inclining in a sort of 

 curve from without inwards. 



Structure. — It has two beginnings. One is pyramidal, elon- 

 gated, and tendinous, and extends high up the radius : the other 

 is triangular and fleshy, and is attached lower down. They both 

 unite to form one fleshy belly, which is intermixed with slips of 

 tendon, and finally ends in a single narrow flattened tendon. 



Action. — To assist the perforans. 



LUMBRICI, ANTERIOR ET POSTERIOR. — I.Umbricalcs. 



Consist of two pairs of pale, delicate, small muscles, having 

 long slender tendons. 



The lumbrici posteriores are to be found invested in adipose 

 membrane, adhering to the inner side of the tendo perforans, 

 about one-third of its lengtli upwards from the fetlock. Here- 

 abouts they are broad ; but they grow narrow as they descend, 

 assuming altogether a pyramidal figure; and they give off" at 

 the fetlock slender flattened tendons, which aj)pear to unite to 

 form the crescentic border of the cellular and tendinous sheath 

 at that part inclosing the tendo perforans. 



The lumbrici anteriores lie within the spaces left between the 

 small metacarpal bones and the suspensory ligament, under 

 u 



