MUSCLES OF THE ANTERIOR LIMBS. 



331 



muscular portion. The fibres composing it are fixed to the posterior surface of 

 the radius, where they are slightly divergent, and collect upon a small particular 

 tendon, which is confounded with the common tendon after contracting adhesions 

 with the radial baud of the perforatus. 



Course and Attachments of the tendon. — The tendon which succeeds these 

 three portions, enters the carpal sheath with that of the superficial flexor. 

 Towards the middle of the metacarpal region, it receives a strong fibrous band 

 from the great posterior ligament of the carpus (Figs. 179, 23 ; 182, 18), 

 traverses the sesamoid annular apparatus of the perforatus tendon, passes 

 between the two terminal branches of that tendon, over 

 the pulley on the posterior face of the second phalanx, 

 and afterwards widens to form a large expansion desig- 

 nated the plantar aponeurosis. 



This aponeurosis glides, by its anterior face, over the 

 inferior surface of the navicular bone, by means of a 

 particular synovial membrane — the navicular sheath — 

 and is covered, posteriorly, by a fibrous layer, noticed for 

 the first time by H. Bouley, who considered it a reinforcing 

 sheath for the perforans tendon. It is finally inserted into 

 the semilunar crest of the os pedis, and the median 

 imprints situated behind this crest, 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- 

 desac of the sesamoid sheath, w^here 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 (Fig. 137, 15, 16). The first is in contact with 

 the posterior cul-de-sac of the synovial membrane of the 

 pedal articulation, and is separated from the inferior sac 

 of the sestimoid 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 pos- 

 terior 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 (Fig. 184, 3, 4), and to the metacarpo-phalangeal sheath by a small 

 median band. The latter passes on to the lower end of the great sesamoid 

 synovial sheath, and divides it into two lobes, which are very visible when the 

 sheath has been distended by injection. 



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

 the external cul-de-sac of the elbow-joint, which sac also covers the other muscles 



FLEXOR TENDONS OF THE 

 PHALANGES IN THE HORSE. 



I, Perforatus teudon ; 2, 

 tendou of the perforans 

 at its exit from between 

 the two branches of the 

 perforatus ; 3, 3, its in- 

 sertion in the semilu- 

 nar crest ; 4, 4, the two 

 lateral bands of its re- 

 inforcing sheath ; 5, 5, 

 fibrous expansion of the 

 metacarpo - phalangeal 

 sheath; 6, 7, 8, its lateral 

 bands ; 9, 9, suspensory 

 ligament of the fetlock. 



