DORSUM OF THE ARM 83 



DORSUM OF THE ARM. 



In this region the following are the structures which require 

 to be studied : 



1. The triceps muscle. 



2. The a. profunda brachii, and the n. radialis (musculo-spiral). 



3. The a. collateral ulnaris superior, and the n. ulnaris. 



4. The posterior branch of the a. collateralis ulnaris inferior. 



5. The m. subancomeus. 



Dissection. The skin has already been removed from the dorsum of the 

 arm. The deep fascia should now be raised from the surface of the m. 

 triceps, and its three heads cleaned and isolated from each other. To 

 place the muscle on the stretch, the inferior angle of the scapula should be 

 raised as high as possible, and the forearm flexed at the elbow-joint. The 

 radial nerve, together with the a. profunda brachii, must at the same time 

 receive the attention of the dissector. They should be followed back- 

 wards between the heads of the triceps, and all their branches should be 

 carefully preserved. 



M. Triceps Brachii (O.T. Triceps). This muscle occupies 

 the entire posterior osteo-fascial compartment of the upper arm. 

 It arises by a long or middle head from the scapula, and by 

 two shorter heads, lateral and medial, from the humerus. The 

 fleshy fibres of these three heads join a common tendon, 

 which is inserted into the top of the olecranon of the ulna. 

 The superficial part of the muscle is, for the most part, formed 

 by the long head and the lateral head of the muscle. The 

 medial head is deeply placed ; only a very small portion of 

 it appears superficially, in the lower part of the arm, on each 

 side of the common tendon of insertion. 



The caput longum of the triceps arises, by a flattened 

 tendon, from the rough triangular impression on the upper 

 part of the axillary border and the lower aspect of the neck 

 of the scapula (Fig. 15, p. 34). This tendon takes origin in 

 the interval between the teres minor and subscapularis 

 muscles. 



The two humeral heads take origin from the posterior aspect 

 of the humerus ; and if it be borne in mind that no fibres arise 

 from the sulcus for the radial nerve and that the groove in- 

 tervenes between the origins of the two heads, their rela- 

 tions will be easily understood. The dissector should provide 

 himself with a humerus, and, having first identified the sulcus 

 for the radial nerve, proceed to map out the areas of attach- 



