148 THE UPPER EXTREMITY 



Dissection. All the muscles around the elbow-joint should be removed. 

 In raising the brachialis and the triceps from the anterior and dorsal aspects 

 of the articulation, some care is required to avoid injury to the anterior and 

 posterior parts of the capsule. It is advisable to remove the supinator 

 last, because it is only when this muscle is completely isolated that a 

 proper idea of its attachments and mode of action can be obtained. 



M. Supinator (O.T. Supinator Brevis). The supinator 

 envelops the proximal part of the body and the neck of the 

 radius, covering it completely, except on its medial side 

 (Figs. 41, 54, pp. ioo, 139). It arises from the deep de- 

 pression distal to the incisura radialis of the ulna, and also from 

 the radial collateral ligament of the elbow and the annular 

 ligament of the radius. From this origin the fibres sweep 

 round the dorsal, lateral, and volar surfaces of the radius, 

 and clothe its body as far distally as the insertion of the 

 pronator teres. The dorsal interosseous nerve traverses the 

 substance of the muscle, and separates it into two layers. 



ARTICULATIONS. 



ARTICULATIO CUBITI (ELBOW-JOINT). 



This joint includes (i) the articulatio humero-ulnaris, (2) 

 the articulatio humero-radialis, and (3) the articulatio radio- 

 ulnaris proximalis. In the humero-ulnar articulation the 

 trochlea of the humerus is grasped by the incisura semi- 

 lunaris of the ulna. In the radio-humeral articulation the 

 capitellum of the humerus rests in the shallow fovea capituli of 

 the radius, and in the proximal radio-ulnar articulation the 

 circumferentia articularis of the head of the radius is held in 

 apposition with the incisura radialis of the ulna by the lig. 

 annulare. 



The joint is surrounded by a capsule which is reinforced at 

 the sides by collateral ligaments ; in addition the interosseous 

 membrane, which passes between the interosseal crests of the 

 radius and ulna, and the oblique cord, which connects the 

 tuberosity of the ulna with the proximal part of the inter- 

 osseous crest of the radius, help to keep the radius and ulna in 

 apposition and are therefore included in the ligaments of the 

 elbow-joint. The ligaments of the elbow-joint are therefore 



1. Capsula articularis. 



2. Lig. collaterale ulnare. 



3. Lig. collaterale radiale. 



4. Lig. annulare radii. 



5. Membrana interossea antibrachii. 



6. Chorda obliqua. 



