34 THE ANATOMY OF THE HORSE. 



The Carpal Sheath (Fig.l) is the tubular passage through which 

 the flexors of the digit are transmitted behind the carpus. It is formed 

 in front by the back of the carpus, covered by the posterior common 

 ligament of that joint. Behind it is bounded in its outer third by 

 the pisiform bone, and in its inner two-thirds by a strong fibrous 

 band representing the anterior annular ligament of the human wrist. 

 This band stretches like an arch from the pisiform bone to the inner 

 side of the carpus. It is continuous above with the deep fascia on 

 the back of the fore-arm, of which it may be considered a thickened 

 portion ; and below it becomes thinner, and is continued as the fascia 

 on the back of the metacarpus {palmar fascia of man). The carpal 

 sheath Js provided with a synovial membrane, which lines it and is 

 reflected over the flexor tendons to facilitate their gliding. If the 

 fibrous band just described be cut, and a probe be passed upwards and 

 downwards within the sheath, an idea of the extent of the synovial sac 

 will be gained. It will be found to extend upwards for two or three inches 

 above the carpus, and downwards as far as the middle of the metacarpus. 



Directions. — The fibrous band should be entirely removed in order to- 

 permit the examination of tne tendons, and of the nerves and blood- 

 vessels which accompany these within the sheath. 



The Metacarpophalangeal or Great Sesamoid Sheath (Fig. 1). 

 This is a second synovial apparatus developed in connection with the 

 flexor tendons. If a vertical incision be made through the superficial 

 flexor just above the fetlock, and a probe passed into the incision, it 

 will enter the synovial cavity, and may be pushed upwards for two or 

 three inches above the fetlock, and downwards as far as the middle of 

 the second phalanx. The synovial membrane lubricates the pulley-like 

 surface formed by the sesamoid bones and the inter-sesamoid ligament, 

 and is reflected on to the tendons. It is supported laterally by a 

 fibrous expansion which, adhering to the superficial flexor behind, is 

 inserted in front by three slips on each side, the highest insertion being 

 into the sesamoid, and the other two into the first phalanx. At its 

 lower extremity this synovial membrane meets that of the navicular 

 sheath, and in front of the same point it is separated from the synovial 

 capsule of the coffin-joint by a kind of partition of yellow fibrous 

 tissue connecting the front of the perforans tendon to the back of the 

 os coronse (Plate 10, Fig. 2). 



The Superficial Flexor tendon (Plates 5, 9, 10, and 11). The 

 tendon succeeds the fleshy portion of the muscle at the lower part of the 

 fore-arm, and it is there reinforced by a fibrous hand which springs from 

 the back of the radius and is sometimes termed the superior carpal liga- 

 ment, in contradistinction to the band which reinforces the tendon of the 

 deep flexor below the carpus. The tendon passes through the carpal 

 sheath in company with and behind the deep flexor, and then descends 



