MUSCLES OF THE ANTESIOB LIMBS. 269 



crest of the os pedis, and the median imprints situated behind this crest, 

 in becoming confounded at its sides with the tissue of the lateral fibro- 

 cartilages. 



The navicular sheath is vesicular in form ; it covers the navicular bone 

 and the single ligament of the pedal articulation, becomes reflected on the 

 plantar aponeurosis in front of this ligament, and ascends to the inferior 

 cul-de-sac of the sesamoid sheath, where it is again reflected and continued 

 by itself. It therefore forms two culs-de-sac, one superior, the other inferior, 

 which are readily perceived in a longitudinal and vertical section of the 

 digital region. The first is in contact with the posterior cul-de-sac of the 

 synovial membrane of the pedal articulation, and is separated from the 

 iuferior sac of the sesamoid sheath by a transverse layer of yellow fibrous 

 tissue which attaches the perforans tendon to the posterior face of the second 

 phalanx. The second is situated beneath the interosseous ligament which 

 unites the navicular bone to the third phalanx. 



The reinforcing sheath of the perforans tendon is formed by a fibrous 

 membrane applied against the posterior face of the plantar aponeurosis. 

 This membrane adheres intimately below, to the expansion it covers, and 

 ends in becoming entirely confounded with it. It is fixed, at its borders, to 

 the inferior extremity of the first phalanx, by means of two lateral bands. 



Relations. — The epitroohlean muscular portion is covered, at its origin, 

 by the external cul-de-sac of the elbow joint, wliich sac also covers the other 

 muscles attached to the epitrochlea — the external and oblique flexors of the 

 metacarpus. It responds, anteriorly, with the radius and radial portion of 

 the muscle ; posteriorly, with the perforatus ; externally, with the external 

 flexor of the metacarpus; inwardly, with the internal and oblique flexors 

 of the same ray. 



The ulnar -portion, covered by the antibrachial aponeurosis, covers the 

 epitrochlean portion. 



The radial division is comprised between the latter and the posterior face 

 of the radius. 



The tendon is in contact, posteriorly, with that of the perforatus ; 

 anteriorly, with the posterior ligament of the carpus, the suspensory ligament 

 of the fetlock, and the sesamoid groove ; by its sides, with the vessels and 

 nerves of the digit. Its terminal expansion is covered by the plantar cushion, 

 which adheres to it, in front, in the most intimate manner ; it covers the 

 navicular bone. 



Action. — This muscle flexes the phalanges on one another and on the 

 metacarpus. It also concurs in the flexion of the entire foot on the fore-arm. 

 The band which attaches its tendon behind the carpus, as well as its phalan- 

 geal reinforcing sheath, gives it the mechanical power necessary to support 

 the angle of the metacarpo-phalangeal articulation and the digital region, 

 while the animal is in a standing posture. 



(In the "Deep Flexor," of M. Chauveau's description, we find included 

 two portions which are separately named and described by Mr. Percivall 

 and Professor Gurlt. These are the ulnaris accessorius and radialis accessorius 

 of the former, and the cvhito-ul-nar and radial branches of the latter. These, 

 in reality, are portions of the perforans, and have been so designated in this 

 treatise. Though arising independently, they terminate vi the perforans 

 tendon before it leaves the carpal sheath, and join with it in flexing the 

 metacarpus and phalanges.) 



