ii4 THE SUPERIOR EXTREMITY 



The lateral head of the triceps arises from the lateral and 

 posterior aspect of the body of the humerus, proximal to the 

 sulcus for the radial nerve. It takes origin, by short tendin- 

 ous fibres, along a line which passes distally from the insertion 

 of the teres minor to the proximal border of the sulcus for 

 the radial nerve. But it derives fibres also from a strong 

 fascial bridge or arch which is thrown over the groove so as 

 to give protection to the profunda brachii artery and the 

 radial nerve. The strength and position of this arch can be 

 estimated by thrusting the handle of the knife distally and 

 laterally in the sulcus for the radial nerve, and along the 

 course of the nerve and artery, under the lateral head of 

 the triceps. By its distal end the arch is connected with the 

 lateral intermuscular septum. 



The medial head of the triceps is placed distal to the sulcus 

 for the radial nerve. Its proximal end, which is narrow and 

 pointed, lies close to the distal end of the insertion of the 

 teres major. The origin gradually widens as the sulcus for 

 the radial nerve passes towards the lateral border of the 

 humerus, and in the distal third of the arm it covers the 

 posterior surface of the humerus from the lateral to the medial 

 border (Fig. 48). It springs also from the posterior surface 

 of the medial intermuscular septum, and from the distal part 

 of the corresponding surface of the lateral intermuscular 

 septum. The medial head of the triceps, therefore, has very 

 much the same origin from the posterior surface of the bone 

 that the brachialis has from the anterior aspect. 



The dissector should now study the common tendon of 

 insertion of the triceps. The long and the lateral heads end 

 in a broad, flat tendon, which is inserted into the back part 

 of the proximal surface of the olecranon, and at the same 

 time gives off, on the lateral side, a strong expansion to the 

 fascia of the forearm as it covers the anconseus muscle. The 

 short fleshy fibres of the medial head are, for the most part, 

 inserted into the deep surface of the common tendon, but a 

 considerable number find direct attachment to the olecranon, 

 whilst a few of the deepest fibres are inserted into the loose 

 posterior part of the capsule of the elbow-joint. The latter 

 fibres have been described as a separate muscle under the 

 name of subanconceus. The triceps is supplied by branches 

 from the radial nerve. It is an extensor of the elbow-joint 

 and an adductor of the arm. 



