THE BRACHIAL MUSCLES. 



585 



and the bursa beneath the infraspinatus often communicate with the shoulder-joint, 

 and disease of the latter may spread to them. 



An infraserratus bursa has been described (Terrillon), situated between the infe- 

 rior scapular angle and the chest-wall. Its enlargement gives rise to friction-like 

 crepitation or creaking, which has been mistaken for fracture of ribs or scapula or 

 for an arthritis of the shoulder. Nancrede says that this symptom is due to (a) an 

 exostosis on the ribs or scapula which has caused such atrophy of the subscapular 

 and serratus magnus muscles as to allow the two bony surfaces to come in contact ; 

 or {d) a localized projection of the ribs due, for example, to a post-pleuritic con- 

 traction of the chest, and with the same muscular atrophy ; or (c) a primary atrophy 

 of the muscles, as in ankylosis of the scapulo-humeral joint, which will admit of the 

 normal scapula and ribs becoming apposed. This latter condition especially causes 

 increased movements of the scapula over the thoracic wall and favors the development 

 of this bursa. 



THE BRACHIAL MUSCLES. 



Pre-Axial. 



1. Biceps 



2. Brachialis anticus. 



Post-Axial. 



1. Triceps. 



2. Anconeus. 



Cephalic vein 



Biceps 



The brachial group includes those muscles which act primarily upon the fore- 

 arm and form the muscular substance of the arm. Some of them, however, take 

 origin in whole or in part from the pectoral girdle and thus hsixe some effect on the 

 movements which occur about the shoulder-joint, although their principal action is 

 upon the forearm. 



The Brachial Fascia. — The deep layer of the fascia of the arm forms a com- 

 plete investment of the muscles of the brachial region. Above it passes over into 

 the thin fascia covering the 



deltoid muscle, and ,me- ^ . ric. 5 9. 



dially it becomes continu- 

 ous with the axillary fascia, 

 while below it is continuous 

 with the fascia of the fore- 

 arm, adhering firmly to the 

 periosteum covering the 

 subcutaneous portions of 

 the humerus and the ole- 

 cranon process, and being 

 reinforced by tendinous 

 prolongations from the bi- 

 ceps and triceps muscles. 



From its lateral and 

 medial surfaces it sends 

 sheet-like prolongations in- 

 ward to be attached to the 

 humerus. These sheets, 

 termed the intermuscular ' 

 septa, are of considerable 

 strength and give attach- 

 ment to adjacent muscles. 

 They pass to the humerus 



between the lateral and medial borders of the triceps and the remammg muscles of the 

 arm, and it is to be noted that, while the medial or inner septum marks the boundary 

 between the pre-axial and post-axial muscles, this is not the case with the lateral or 

 external septum. In the lower part of their extent the septa are attached to the supra- 

 condylar ridges of the humerus and terminate at the condyles, a number of post-axial 

 muscles of the forearm arising from the outer condyle anterior to the external septum. 



A number of subcutaneous bursae occur between the integument and the bra- 

 chial fascia in those regions in which the fascia is adherent to the subjacent perios- 

 teum covering so-called subcutaneous portions of the skeleton. Thus there is a 



Superficial 

 Deep fasc 



Musculo- 



spiral nerve 



Brachio- 



radialis 



External 



intermuscular 



septum 



Humerus 



Musculo- 

 utaneous nerve 



Brachialis 

 anticus 



Brachial 



vessels 



Median nerve 



Basilic vein 



Internal 



intermuscular 



septum 



Ulnar nerve 



Triceps, inner 

 head 



Triceps, outer head 



Triceps, middle head Tendon of triceps 



Section across right arm in lower third. 



