DORSUM OF THE ARM 85 



narrow pointed fleshy slip, which obtains origin from the 

 bone as high as the insertion of the teres major muscle. 

 Below, it widens out and arises, by short fibres, from the entire 

 breadth of the posterior surface of the humerus. It also 

 springs from the posterior surface of the medial intermuscular 

 septum, and from the lower 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 back of the bone that the brachialis has from the anterior 

 surface of the bone. 



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 anconaeus 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. These latter 

 fibres have been described as a separate muscle under the 

 name of subanconceus. . The triceps is supplied by branches 

 from the radial nerve. 



Dissection. In order that the radial nerve and the art. profunda brachii 

 may be fully exposed, the lateral head of the triceps must be divided. 

 Thrust the handle of a knife along the sulcus for the radial nerve, and 

 under the muscle. This will give the direction in which the lateral head 

 of the triceps should be severed. Beyond cleaning the nerve and its 

 branches, and the art. profunda brachii, as they lie in the groove, no further 

 dissection is necessary. 



Nervus Radialis (O.T. Musculo-Spiral Nerve). The radial 

 nerve is the direct continuation of the posterior cord of the 

 brachial plexus after it has furnished in the axilla the two 

 subscapular nerves, the thoracodorsal nerve, and the axillary 

 nerve. In the first instance, the radial nerve proceeds distally, 

 behind the distal part of the axillary artery and the proximal 

 part of the brachial artery. It soon leaves the anterior aspect 

 of the arm, however, and, inclining backwards, with the art. 

 profunda brachii, enters the interval between the long and the 

 medial heads of the triceps, and reaches the sulcus for the radial 

 nerve. In this it passes round the back of the body of the 

 16* 



