THE ARM. 



271 



Outer head 

 of triceps 



THE INTERMUSCULAR SEPTA. 



The deep fascia of the arm completely encircles it, like a tube. It is continuous 

 above with the fascia covering the deltoid, pectoralis major and teres major muscles, 

 and axillary fascia. Below, it is continuous with the fascia of the forearm and is 

 attached to the olecranon and internal and external condyles. 



On each side of the lower half of the humerus, extending from the condyles and 

 the bone above outward to the deep fascia, are two fibrous partitions. They are 

 the internal and external intermuscular 

 septa. The space in front of them is filled 

 by the flexors, the biceps, and brachialis 

 anticus, and the space behind contains 

 the triceps extensor. The external sep- 

 tum begins at the external condyle and 

 extends above to the tendon of the del- 

 toid, with which it blends. The internal 

 septum begins below at the internal con- 

 dyle and extends above to the coraco- 

 brachialis. The radial (musculospiral) 

 nerve and anterior terminal branch of 

 the (superior) profunda artery, as they 

 wind around the humerus below the in- 

 sertion of the deltoid, pierce the external 

 septum. The internal septum is pierced 

 high up by the ulnar nerve and superior 

 ulnar collateral (inferior profunda) artery 

 as they emerge at about the level of the 

 lower portion of the insertion of the 

 coracobrachialis to pass down behind 

 the internal condyle. 



These intermuscular septa are of 

 importance in operative procedures be- 

 cause they indicate the limits of the mus- 

 cles and position of nerves and vessels. 



SURFACE ANATOMY. 



Inasmuch as the movements of the 

 elbow -joint are anteroposterior only and 

 not lateral, the muscles are principally 



on the front and back and not on the "> . HS^ / Anconeus 



sides. Hence on looking at an arm 

 a rounded mass is seen anteriorly and 

 posteriorly, and separating them on the 

 sides can be seen in a spare, muscular 

 individual, distinct furrows called the 

 internal and external bicipital furrows. 

 If these furrows are obscured by fat, 

 one can still feel that the bone is nearer 

 the surface at these points than else- 

 where. The anterior muscle mass is 

 formed by the biceps and brachialis 



anticus muscles, the posterior mass by the triceps. The bone is most readily 

 felt at the insertion of the deltoid at the middle of the outer side of the arm. 

 From this point directly down to the external condyle passes the external inter- 

 muscular septum and external bicipital furrow. Winding around from the poste- 

 rior edge of the insertion of the deltoid is the radial (musculospiral} nerve and 

 {superior) profunda artery. They pierce the external intermuscular septum and 

 pass downward in the groove formed by the brachioradialis (supinator longus) and 

 extensor muscles on the outside and the brachialis anticus on the inside. On the 

 inner side of the arm the bicipital furrow, between the biceps in front and the triceps 



FIG. 283. Triceps and anconeus muscles. 



