FRONT OF THE ARM 71 



of the biceps brachii. The latter fibres constitute the lacertus 

 fibrosus, and form a very distinct band (O.T. semilunar 

 or bicipital fascia) which, continuous with the fascia above 

 and below, bridges across the brachial artery, and is lost upon 

 the pronator teres muscle on the medial side of the forearm. 



The fascia brachii may be reflected by making an incision through 

 it along the medial line of the front of the arm. In throwing the medial 

 portion medially, the dissector must leave the lacertus fibrosus in 

 position. This may be done by separating it artificially from the general 

 aponeurosis by an incision above and below it. 



Medial inter- 

 muscular septum 



Lateral inter- 

 muscular septum 



FIG. 29. Diagram (after Turner) to show how the Arm 

 is divided by the intermuscular septa and bone into an 

 anterior and posterior compartment. These compartments 

 are represented in transverse section. 



As the foregoing dissection is proceeded with, it becomes 

 evident that septa or partitions pass in between the muscles 

 from the deep surface of the investing fascia brachii. Two 

 of these possess a superior strength, and obtain direct attach- 

 ment to the humerus. They are the lateral and medial 

 intermuscular septa. The connections of these cannot be 

 fully studied at present, but it is important that the student 

 should understand their relations at this stage. In the course 

 of the dissection of the arm they will gradually be displayed. 



The septum intermusculare mediale is the stronger and more 

 distinct of the two. It is attached to the medial epi- 

 condylar ridge, and may be followed proximally as high as 

 the insertion of the coraco-brachialis muscle. The septum 

 intermusculare laterale is fixed to the lateral epicondylar 



