THE BRACHIAL REGION. 141 



aponeurosis completely envelops the arm, and is thickest 

 at the back and sides ; it is continuous above with that 

 covering the deltoid and subclavicular region, and below 

 with that covering the forearm, and sending processes 

 between the muscles forms septa, which are attached to 

 the humerus. The attachment of this aponeurosis is 

 very evident laterally, where it is inserted into the 

 condyles and condyloid ridges of the humerus, dividing 

 the region into two distinct compartments, an anterior 

 and a posterior. The anterior contains, successively, 

 the biceps, immediately beneath which, in the lower 

 half of the arm, is the brachialis anticus, inclosing at 

 the upper part of its origin, the insertion of the deltoid, 

 and passing downwards to its own insertion, covers 

 in the humerus completely between the lateral margin 

 of the anterior and posterior compartments. Behind, 

 and internal to the biceps above, is the coraco-brachi- 

 alis; below and externally are, the musculo-spiral nerve, 

 the origins of the supinator longus and extensor carpi 

 radialis longior. 



Lying along the inner border of the biceps is the 

 vasculo-nervous cord, formed by the brachial artery, its 

 veins, and the median, ulnar, external, and internal 

 cutaneous nerves; the median accompanies the artery 

 throughout, lying first outside it, then upon it, and lastly 

 internal. In the upper third, this vasculo-nervous cord 

 lies along the inner border of the coraco-brachialis, having 

 the long head of the triceps behind, and just on the 

 humerus, against which the vessel is easily compressed ; 

 in its lower two-thirds it lies on the brachialis anticus. 



The posterior aponeurotic compartment contains the 

 triceps, which covers in the entire posterior surface of 

 the humerus and the musculo-spiral nerve before it passes 



