SUPIXATOE EADII LONGUS. 



215 



qnadratus. Only one half of the flexor profundus digitonini is supplied mth 

 nerves from the median, the other half, together with the whole of the flexor 

 carpi ulnaris receives twigs from the ulnar nerve. 



SUPINATOR AND EXTENSOE MUSCLES. 



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

 divided into a superficial and a deep layer. 



The SUPERFICIAL MUSCLES are six in num- 

 ber, viz., the supinator longus, the exten- 

 sores carpi radiales longior and brevior, 

 the extensor coaimunis digitorum, extensor 

 minimi digiti, and extensor carpi ulnaris. 



The supinator radii longus muscle 

 arises from the upper two-thirds of the ex- 

 ternal ridge of the humerus, and the ex- 

 ternal inter-muscular septum. Its fibres 

 form a thin fleshy mass which descends 

 upon the anterior and outer border of the 

 forearm, about the middle of which they 

 end in a flat tendon, which is inserted 

 into the external border of the radius, near 

 the base of the styloid process. 



Fig. 176. — Superficial Muscles of the Forearm 

 AXD Hand, seen frou behind. (A. T.) | 



(J, olecranon ; e, external condylar eminence ; /, 

 lower end of the ulnar ; S, main tendon of the triceps 

 extensor cubiti ; 8", its inner liead ; 9, anconeus; 10, 

 part of brachialis anticiis ; 11, supinator longus; 12, 



extensor carpi radialis longior; 13, brevior; 



14, extensor communis digitorum ; 15, extensor carpi 

 ulnaris ; 15', its insertion into the fifth metacarpal 

 bone ; +, between 14 and 15, extensor minimi 

 digiti ; 16, origin of the Hexor carpi ulnaris by an 

 aponeurosis from the back of the ulna; 17, extensor 

 ossis metacarpi pollicis : 17', its insertion into the 

 iirst metacarpal bone ; IS, extensor primi internodii 

 pollicis ; IS', its insertion into the first phalanx ; + 

 and J, posterior annular hgament of the carpus or 

 retinaculum of the extensor tendons ; at +, the ten- 

 dons of the long and short radial extensors ; at + , 

 the tendon of the extensor minimi digiti ; 19, tendon 

 of the extensor secundi internodii ; 20, is placed on 

 the proximal end of the second metacarpal bone, close 

 to the insei-tion of the radial extensors of the carpus : 

 in the hand, the dorsal interossei muscles are shown, 

 and on the middle finger the insertion of the exten- 

 sor tendons. 



Rlationx. — This muscle is covered only by 

 skin and fascia, except at its insertion, where 

 two of the extensor tendons of the thumb lie 

 superficial to it. Above, the brachialis anticus is 



in contact with its inner siu-face and the radial extensors of the cariras are 

 beneath it. It fonns the outer boundary of the triangular space at the bend of the 

 elbow, and in the forearm it rests upon the supinator brevis, flexor sublimis 

 digitorum, pronator teres, radial artery, musculo-spiral and radial nen-es. 



Varieties. — These are neither great nor numerous in this muscle. One of the 



