378 



THE MUSCULATURE 



They extend the forearm. 



by branches of the radial (musculo-spiral) nerve. 

 The long head is also an adductor of the arm. 



The triceps, variously modified, is found in the amphibia and all higher vertebrates. The 

 anconeus is found in the prosimians and all higher forms. The triceps muscle is homologous 

 with the quadriceps of the thigh. The long head is equivalent to the rectus femoris. The 

 anconeus is not represented in the lower limb. 



The triceps brachii (figs. 355, 356, 363). — The long head anses from the infraglenoid tuber- 

 osity of the scapula by a strong, broad tendon, some of the fibres of which are connected with 

 the inferior portion of the capsule of the shoulder-joint. The tendon soon divides into two 

 lamellae, which extend distally, one a short distance on the deep surface, the other much farther 



Fig. 363. — Dorsal View of the Scapular Muscles and Triceps. 



Supraspinatus 



Infraspinatus 

 Teres minor 



Teres major 



Site of appearance of radial nerve at 

 the back of the arm 



Long head of triceps 



Lateral head of triceps 



Medial head of triceps 



Anconeus 



on the .superficial surface of this head. The parallel fibre-bundles which arise from these 

 lamella; form a thick muscle-band which twists upon itself so that the ventral surface at the 

 origin becoiiuis dorso-medial at the insertion. At the insertion the long head becomes ap- 

 plied to an ajjoiicurosis which extends upward from the main tendon of insertion of the triceps. 

 '1 he fibrc-buiKlk's extend for .some distance on the medial side of this tendon and terminate 

 about tlircc-fourtlis (;f the way down the arm. 



The lateral head has a tendinous oriqin from the superior lateral portion of the posterior 

 Hurfac(! of the humerus along a line extending from the insertion of the teres minor as far as the 

 groove for the radial (nuisculo-spiral) nerve, and from the aponeurotic arch formed by the 

 lateral intermuscular .septum as it crosses this groove. The constituent fibre-bundles descend, 

 th«! superior vertically, the inferior oblicpiely, to be inserted on the dorsal and ventral surfaces 

 of the proximo-lnterjil margin of the conunon tendon of insertion of the triceps. 



Tlie medial head has a fleshy ori.(/in from the posterior surface of the humerus below the 

 r:i(lial ^nnisfulo-spiral) groove and from the dorsal surfaces of the medial and lateral intermus- 

 ••iil;ir .septa. The greater part of the fibre-hiiiidkis arising from this extensive area are inserted 

 into the deep surface of the common tendon, but some extend directly to the olecranon and the 

 arti( iil:u- capsule of the elbow. The slip attached to the capsule is sometimes called the 

 subanconeus muscle. 



