588 



HUMAN ANATOMY. 



(b) THE POST-AXIAL MUSCLES. 

 I. Triceps (Figs. 570, 572). 



Attachments. The triceps (m. triceps brachii) is a strong muscle which occu- 

 pies the entire dorsal surface of the arm. It arises by three heads. The scapular or 



Fig. 572. 



Supraspinatus 



Spine of scapula 



Acromion process 



Head of humerus covered by 

 capsular ligament 



Infraspinatus 



Infraspinatus, 

 cut edge 



Teres minor (cut) 



Inferior angle of 

 scapula 



Tendon of insertion of teres 

 minor 



Axillary border ol 

 scapula 



Pectoralis 

 major 



Triceps, 

 ong heaa 



Triceps, 

 outer head 



Teres major 

 Serratus magnus 



Triceps 



Latissimus dorsi 



long head takes its origin by a tendon from the infra- 

 glenoid tuberosity of the scapula ; the inner or medial 

 head, from the posterior (dorsal) surface of the humerus 

 and from both intermuscular septa below and medial 

 to the groove for the musculo-spiral nerve ; and the 

 outer or lateral head, from the external intermuscular 

 septum and the posterior surface of the humerus above 

 and lateral to the groove for the musculo-spiral nerve. 

 The three heads unite to form a strong, broad tendon 

 which is inserted into the olecranon process of the 

 ulna. The common tendon of insertion begins as a 

 broad aponeurosis upon the anterior surface of the 

 long head, the fibres of which are attached to the 

 upper border and the upper part of the posterior sur- 

 face of the aponeurosis. The fibres of the lateral head 

 are attached to the lateral border of the aponeurosis, 

 while those of the medial head, which is much stronger 

 than the lateral one, pass to its anterior surface. 



Nerve-Supply. — By the musculo-spiral nerve 

 from the sixth, seventh, and eighth cervical nerves. 



Action.— To extend the forearm on the upper arm and to draw the entire arm^ 

 backward. 



Variations.— The triceps occasionally possesses an additional head arising either from the 

 coracoid process of the scapula or from the capsule of the shoulder-joint. 



Triceps and posterior scapular mus- 

 cles ; portions of infraspinatus and teres 

 minor cut away. 



