24 THE ANATOMY OF THE HORSE. 



Action. — Like the preceding two muscles. 



Directions. — The three flexors of the metacarpus surround the flexors 

 of the digit, and they should be cut about their middle and reflected to 

 bring these latter into view. 



The Superficial Flexor of the Digit (flexor pedis perforatum) (Plate 

 6) arises, by a tendon common to it and the deep flexor, from the 

 lower extremity of the inner condyle of the humerus. Its muscular 

 belly contains much tendinous tissue, and cannot without difficulty be 

 separated from the deep flexor, on which it rests. At the lower part 

 of the radius its muscular portion is succeeded by a tendon, which, 

 after being reinforced by a fibrous band from the back of the radius, 

 passes through the carpal sheath behind the carpus, and is ultimately 

 inserted by a bifid tendon into the second phalanx. The examination of 

 this and the succeeding muscle from the carpus downw T ards must be 

 postponed till the dissection of the metacarpus and digit is undertaken. 

 Action. — The muscle flexes successively the pastern, fetlock, and 

 carpal joints. 



The Deep Flexor of the Digit (flexox pedis perforans) (Plate 6). 

 This muscle is situated in contact with the posterior surface of the 

 radius, and consists of three divisions, which may be distinguished as 

 the humeral, the radial, and the ulnar portions. The humeral or main 

 division arises, in common with the preceding muscle, from the lower 

 extremity of the inner condyle of the humerus. The radial portion, or 

 radialis accessorius, is deeply placed, and arises from the back of the 

 radius. The ulnar division, or ulnaris accessorius, is placed beneath 

 the deep fascia of the fore-arm, where it lies between the external and 

 oblique flexors of the metacarpus, and is accompanied by the ulnar 

 nerve and vessels. It arises from the summit and posterior border of 

 the olecranon. These three divisions unite above the carpus, and have 

 a common tendon which passes through the carpal sheath, and is 

 ultimately inserted into the os pedis. 



Action. — It flexes successively from below upwards the inter-phalan- 

 geal joints, the fetlock, and the carpus. 



Directions. — The front of the fore arm must now r be dissected ; and 

 here it will be convenient to turn attention in the first place to muscles ; 

 but, while these are being isolated, care is to be taken of the interosseous 

 vessels, which descend along the lateral extensor at the outer side of the 

 region, and of the tendon of the oblique extensor where it crosses over 

 the tendon of the extensor metacarpi magnus above the carpus. 



The Extensor Metacarpi Magnus (Plates 7 and 8) corresponds to 

 the long and short radial extensors of the wrist in the human subject. 

 It is a powerful muscle, having at its upper end a massive muscular 

 belly, which tapers downwards, and terminates a few inches above the 

 carpus in a tendon. It arises from the anterior edge of the outer 



