DISSECTION OF THE ANTERIOR LIMB. 



33 



Tlie tendon is finally inserted into the pyramidal process of the os 

 pedis. 



Action. — The first action of the muscle is to extend the third 

 phalanx on the second, and then 

 the second on the first. When con- 

 traction is continued, it produces 

 successively extension of the fet- 

 lock and of the carpus. 



Directions. — The tendons on the 

 back of the metacarpus and digit ^ 

 must next be dissected ; and as 

 a preliminary step, the carpal , 

 and metacarpo-phalangeal sheaths 

 formed in connection with these 

 tendons should be examined. 



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 meta- 

 carpus (^palmar fascia of man). 

 The carpal sheath is provided with 



Dissection of the Metacarpus and Digit, showing the Tendons and their Synovial 

 Sheaths (Chauveau). 

 1. Synovial bursa of the extensor metacarpi magnus ; 2. Superior cul-de-sac, or pouch, of the 

 synovial membrane of the carpal sheath ; 2', 2'. Inferior part of the same ; 3. Pouch of theradio- 

 cjirpal synovial membrane, appearing as a hernia between the posterior common ligament and the 

 outermost radio-carpal ligament ; 4. Synovial bursa of the extensor pedis ; 5. Protrusion of the 

 synovial membrane of the fetlock -joint ; 6, 7, 8. Superior, middle, and inferior p'ouches of the 

 synovial membrane of the metacarpo-phalangeal sheath ; 9. Inferior extremity of the same, exposed 

 by the removal of the reinforcing sheath of the perforans tendon ; E. S. Extensor suffraginis ; S. L. 

 Subcarpal ligament ; E. P. Extensor pedis ; S. S. Superior sesamoidean (suspensory) ligament ; F. 

 Pa. Flexor perforans ; F. Pt. Flexor perf oratus. 



D 



