SUPINATOR AND EXTENSOR MUSCLES. 229 



the trapezium, magnum, or some other part of the carpus, or into one or more of the meta- 

 carpal bones. 



Nerves. The pronator and flexor muscles of the forearm receive their nerves mostly 

 from the median, only one, the flexor carpi ulnaris (8 c, 1 d), being wholly, and another, the 

 flexor profundus digitorum (8 c, 1 d), in part supplied from the ulnar nerve by branches 

 entering them near the elbow. The pronator radii teres (6 c), flexor carpi radialis (6 c), 

 palmaris longus, and -the condylo-ulnar head of the flexor sublimis digitorum (7, 8 c, 1 d) 

 receive branches from the median in the neighbourhood of the elbow, while the radial head 

 and the index finger belly of the flexor sublimis have separate twigs from the same trunk. 

 The flexor longus pollicis (8 c, 1 d), pronator quadratus (8 c, 1 d), and outer half of the flexor 

 profundus digitorum are supplied by the anterior interosseous branch of the median. The 

 outer two lumbricales are innervated by the median, and the inner two by the uinar. 



SUPINATOR AND EXTENSOR MUSCLES. 



The muscles of this group are, like those of the front of the forearm, divided into 

 n superficial and a deep group. 



The SUPERFICIAL MUSCLES are seven in number, viz., the supinator longus, the 

 extensores carpi radiales longior and brevior, the extensor communis digitorum, ex- 

 tensor minimi digiti, extensor carpi ulnaris, and anconeus. The last muscle has 

 already been described in connection with the triceps (p. 221). 



The supinator radii longus muscle (brachio-radialis) arises from the upper 

 two-thirds of the external supracondylar ridge of the humerus, and from the external 

 intermuscular septum. Its fibres form a thin fleshy mass, which descends on the outer 

 and anterior part of the limb to about the middle of the forearm, where it ends in 

 a flat tendon, which is inserted into an impression on the outer side of the lower end 

 of the radius, near the base of the styloid process. 



Relations. This muscle is covered only by skin and fascia, except at its insertion, where 

 two of the extensor tendons of the thumb lie over the tendon. Above, the brachialis anticus 

 is in contact with its inner surface, the musculo-spiral nerve being interposed, and the long 

 radial extensor is beneath it. It forms the outer boundary of the triangular space at the bend 

 of the elbow, and in the forearm it rests upon the supinator brevis, pronator teres, flexor 

 sublimis digitorum, and the radial vessels and nerve. 



Varieties. The supinator longus is often united at its origin with the brachialis anticus. 

 The tendon is occasionally divided into two or even three slips, which are inserted either 

 together or at some distance from each other. In rare cases complete doubling of the muscle 

 has been seen. Insertion, partial or complete, into the middle of the radius, fasciculi to the 

 tendon of the biceps, the tuberosity or anterior oblique line of the radius, slips of communica- 

 tion with the extensor carpi radialis longior or extensor ossis metacarpi pollicis, and absence 

 of the muscle have also been observed. 



The extensor carpi radialis longior muscle arises from the lower third of the 

 external supracondylar ridge of the humerus, and from the external intermuscular 

 septum : a few fibres also spring from the outer side of the common tendon of the 

 extensor muscles. Its muscular belly ends above the middle of the forearm in a flat 

 tendon, which passes, conjointly with that of the following muscle, in the outermost 

 of the grooves on the posterior surface of the radius, and is inserted into the base of 

 the second metacarpal bone. 



The extensor carpi radialis brevior muscle arises from the outer condyle of 

 the humerus by a tendon common to it and the following muscles, from the inter- 

 vening fibrous septa, from the fascia covering it, and from the external lateral 

 ligament of the elbow-joint. Its muscular belly ends in a tendon, which, descending 

 with that of the extensor longior, passes through the same groove of the radius with 

 it, and is inserted into the base of the metacarpal bone of the middle finger. 



Relations. Of the two foregoing muscles the extensor longus is the more superficial. 

 The extensor brevis covers the supinator brevis and the insertion of the pronator radii teres. 

 The tendons of these muscles are crossed obliquely above the annular ligament by the 



Q 2 



