FASCIA AND MUSCLES OF THE FOREARM AND MANUS 263 



extensor (in front) and the lateral extensor and flexor carpi externus (behind); 

 (6) one between the common extensor and the extensor carpi radialis; (c) one be- 

 tween the inner and middle flexors of the carpus. 



The carpal fascia (Fascia carpi) is a direct continuation of that of the forearm. 

 It is attached chiefly to the tuberosities at the distal end of the radius, to the ac- 

 cessory carpal (pisiform) bone, and to the lateral ligaments. In front it forms the 

 so-called anterior annular ligament (Ligamentum carpi dorsale), bridging over the 

 grooves and binding dov/n the extensor tendons and their synovial sheaths. Be- 

 hind it is greatly thickened and forms the posterior annular or transverse liga- 

 ment of the carpus (Ligamentum carpi transversum). This stretches across from 

 the accessory carpal bone to the internal lateral ligament and the proximal 

 extremity of the inner metacarpal bone. It thus completes the carpal canal, in 

 which lie the flexor tendons, their synovial sheath, and the principal vessels and 

 nerves of the region. 



The fascia of the metacarpus and digit (Fascia metacarpea et digitalis) is, in 

 general, thinner than the preceding. It is attached to the tendons, ligaments, and 

 the exposed bony prominences — especially to the small metacarpal bones. On the 

 flexion surface of the fetlock joint it is much thickened by fibers passing transversely 

 from one sesamoid lione to the other, forming an annular ligament which binds down 

 the flexor tendons in the sesamoid groove or canal. Distal to this is a second thick 

 quadrilateral sheet (Ligamentum vaginale) which covers and is adherent to the 

 tendon of the flexor perforatus. It is attached on either side by two bands to the 

 borders of the first phalanx, thus firmly binding down the flexor tendons. A little 

 further down a crescentic fibre-elastic sheet covers the terminal expansion of 

 the deep flexor tendon. It is attached on either side by a strong band to the 

 side of the first phalanx about its middle. 



A. Extensor Dfvision 



1. Extensor carpi radialis (M. extensor carpi radialis s. radialis dorsalis; ex- 

 tensor metacarpi magnus; anterior extensor of the metacarpus). — This is the 

 largest muscle of the extensor division, and lies on the anterior (dorsal) surface of 

 the radius. 



Origin. — (1) The external condyloid crest of the humerus; (2) the coronoid 

 fossa. 



Insertion. — The tuberosity on the anterior (dorsal) surface of the proximal 

 extremity of the large (third) metacarpal bone. 



Action. — To extend and fix the carpal joint and to flex the elbow joint. 



Structure. — The belly of the muscle is rounded, and runs out to a point at the 

 distal third of the forearm. The tendon, which runs nearly the whole length of the 

 fleshy portion, appears on the surface of the latter about its middle; here the muscle 

 shows a distinctly pennate arrangement. The tendon passes through the middle 

 groove at the distal extremity of the radius and over the capsule of the carpal 

 joint, bound down by the anterior annular ligament and invested with a synovial 

 sheath. The latter begins three to four inches (ca. 8 to 10 cm.) above the carpus 

 and extends almost to the insertion of the tendon. In the lower half of the forearm 

 the deep fascia blends with the tendon, and here the latter is joined by the long 

 tendon of the biceps. 



Relations. — Superficially, the skin, fascia, and the oblique extensor; deeply, 

 the capsule of the elbow joint, the biceps tendon, the radius, the carpal joint capsule, 

 the anterior radial artery, and the radial nerve; externally, the anterior or com- 

 mon extensor; internally, at the elbow, the brachialis and biceps. 



Blood-supply. — Anterior radial artery. 



Nerve-supply. — Radial nerve. 



2. Anterior or common digital extensor (M. extensor digitalis communis; 



