314 THE MUSCLES 



sides consisting of the deep fascia and the intevninscular septa which intervene 

 between it and the adjacent muscles. The fleshy tilires converge downAvards and 

 somewliat outwards ujion the back of the tendon which begins at the junction of 

 the upper and middle thirds of the forearm, and is free a little below the middle 

 of the forearm. 



At tlie wrist the tendon ixisses througli a special compartment external to the 

 tube formed l)y the anterior annular ligament. This compartment is bounded 

 Itehind l)y the scaphoid bone and the groove upon the trapezium; externally, by 

 the tul)erosity of the scaphoid ])one and the ridge upon the trapezium; and in front 

 and internally by a thickening of the deep fascia of the forearm. It is lined by a 

 special synovial membrane. 



Nerve-supply. — From the outer and inner cords of the brachial plexus 

 (through the sixth cervical nerve) by filaments from the median nerve which pass 

 to its posterior surface in its upper third. 



Action. — (1) To flex the wrist. By its insertion into the metacarpus it bends 

 not only the radio-carpal joint (which is the wrist-joint proper), but also the inter- 

 carpal and the carpo-metacarpal joints, which really take part in all the movements 

 of what may be called the irrist as distinguished from the vrist-joint. (2) ^^"hen 

 the hand is fully supinated, it helps in pronation. (3) It is also a feeble flexor of 

 the elbow. 



Relations. — Superficially, the deep fascia and the superficial veins; deeply, the 

 flexor sublimis digitorum, the flexor longus pollicis, the median nerve, the wrist 

 and some of the carpal joints; on the outer side of it lie the pronator radii teres and 

 the radial vessels; on the inner side it is in contact above with the palmaris longus. 



Variations. — The flexor carpi radialis may have a second origin fi'om the tendon of the biceps 

 or the radius, and its insertion may be extended to the base of the fourth metacarpal bone or to 

 some of the bones of the carpus. It is sometimes absent. 



3. PALMARIS LOXGUS 



The palmaris longus — named from its length and its insertion upon the palm 

 of the hand — is flat and fusiform. 



Origin. — (1) The common tendon from the front of the internal condyle; (2) 

 the deep fascia of the forearm; and (3) the septa which lie lietween the muscle and 

 the flexor carpi radialis, the flexor carpi ulnaris, and the flexor sul)limis digitorum. 



Insertion. — (1) The upper end of the strong central portion of the palmar 

 fascia; (2) the lower pai"t of the front of the anterior annular ligament; and (3) 

 the deep fascia covering the thenar eminence. 



Structure. — Like the preceding muscle it consists of flesh}^ fibres which rise in 

 a long four-sided pyramid from the aponeurotic case formed by the deep fascia and 

 the intermuscular septa. Its tendon appears first upon the anterior surface of the 

 muscle at the junction of the middle and upper thirds of the forearm, and is free 

 about the middle of the forearm. It passes almost directly downwards to the 

 middle of the wrist, where it descends in front of the upper part of the anterior 

 annular ligament, and then becomes attached to its lower edge as well as the 

 adjacent fascite. 



Nerve-supply. — From the outer and inner cords of the brachial plexus 

 (through the eighth cervical nerve) by filaments from the median nerve which enter 

 the deep surface of the muscle. 



Action. — (1) To flex the wrist; (2) to a slight extent to flex the elbow also; 

 (3) it makes tense the central portion of the palmar fascia, so that when an object 

 is grasped finnly by the fingers no injurious pressure is exerted upon the important 

 vessels and nerves which lie beneath that structure; (4) its attachments to the fascia 

 of the thenar eminence gives a firm origin to some of the short muscles of the 

 thumi). 



Relations. — Superficially, the deep fascia and sui)erficial veins; dee])ly. the 

 flexor sublimis digitorum and median nerve, and the upi)er part of the anterior 

 annular liirament. 



