8S ANATOMY IN A NUTSHELL. 



A.< riON. Extends forearm. 



\i.i,\ i. Supply. Seventh and eighth cervical through the musculo-spiral, 



Blood Supply. Radial and superior profunda. 



LESSON XXI. 



Supinator brevis. — Description. — (Plate XXXIII.) — This is a broad mus- 

 cle of hollow cylindrical form, curved round the upper third of the radius. 

 It consists of two distinct planes of muscular fibers, between which lies the 

 posterior interosseous nerve. The two planes arise in common. The fibers 

 of the deeper plane form a sling-like fasciculus, which encircles the neck of 

 the radius above the tuberosity. Between the insertion of the two planes 

 the posterior interosseous nerve lies on the shaft of the bone. 



Origin— The superficial plane by tendinous and the deep by muscular 

 fibers from tl) the external condyle of the humerus; (2) external lateral lig- 

 ament of elbow-joint; (3) orbicular ligament of radius; (4) oblique ridge of 

 ulna; (5) triangular depression in front of the ridge; (6) tendinous expansion 

 covering the surface of the muscle. (Plates XXIII-XXIV.) 



Insertion. The superficial fibers into the outer edge of the bicipital 

 tuberosity and oblique line of the radius; the deeper fibers into the posterior 

 and external surface of the shaft, midway between the oblique line and head of 

 the bone, except the sling-like fasciculous which is attached to the back part of 

 the inner surface of the radius. (Plate XXIV.) 



A.CTION.— Stipulates hand. 



Nerve Supply. Posterior interosseous. 



Blood Supply Interosseous and radial arteries. 



Extensor ossis metacarpi pollicis. — Description. — (Plate XXXIII). — This 

 is the mosl external and the largest of the deep extensor muscles. It lies im- 

 mediately below the supinator brevis, with which it is sometimes united. From 

 its origin it passes obliquely downward and outward and terminates in a 

 tendon which runs through a groove on the outer side of the styloid processof 

 the radius. The tendon of the Extensor brevis pollicislies in the samegroove. 

 The Extensor pollicis occasionally gives off two slips near its insertion, one 

 to the trape/.ium. and the other to blend with the origin of the Abductor 

 pollicis. 



Origin. From outer part of posterior surface of shaft of ulna below in- 

 sertion of Anconeus, from the interosseous membrane, and from the middle 

 third of the posterior surface of shafl of radius. (Plate XXIV.) 



Insertion. Base of metacarpal bone of thumb. (Plate XXVII.) 



Action. Extends thumb. 



Nerve Si pply. Posterior interosseous. 



Bl< Si pply. Posterior interosseous. 



Extensor brevis pollicis. Description. (Plate XXXIII.) — The Exten- 

 sor brevis pollicis (Extensor primi internodii pollicis,) the smallest muscle of 

 this group, lies on the inner side of the preceding, having a similar direction 

 and passing through the same groove on tin 1 outer side of the styloid process. 



