The palmaris longus - named from its length and its insertion upon the palm bf the hand - is flat and fusiform.
The common tendon from the front of the internal condyle ;
the deep fascia of the forearm ;
and the septa which lie between the muscle and ihe flexor carpi radialis, the flexor carpi ulnaris, and the flexor sublimis digitorum.
The upper end of the strong central portion of the palmar fascia ; '
the lower part of the front of the anterior annular ligament ;
and the deep fascia covering the thenar eminence.
Like the preceding muscle it consists of fleshy fibres which rise in 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 nuscle at the junction of the middle and upper thirds of the forearm, and is free about jhe middle of the forearm. It passes almost directly downwards to the middle of jthe 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 fasciae.
From the outer and inner cords of the brachial plexus (through fjhe eighth cervical nerve) by filaments from the median nerve which enter the deep surface of the muscle.
To flex the wrist ;
to a slight extent to flex the elbow also ;
it makes tense the central portion of the palmar fascia, so that when an object is grasped firmly by the fingers no injurious pressure is exerted upon the important vessels and nerves which lie beneath that structure ;
its attachments to the fascia of the thenar eminence gives a firm origin to some of the short muscles of the thumb.
Superficially, the deep fascia and superficial veins ; deeply, the flexor sublimis digitorum and median nerve, and the upper part of the anterior annular ligament.
The palmaris longus is very variable. It may be double, and it is often absent. The fleshy belly is sometimes below, and the tendon in part or entire above. It may take an additional head from the radius or the coronoid process. Its insertion may be into tbe fascia of the forearm, the flexor carpi ulnaris, the short muscles of the little finger, or one of the carpal bones.
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