1 88 ATLAS AND TEXT-BOOK OF HUMAN ANATOMY. 



Fig. 270. — The deltoid and muscles of the upper arm seen from the side. 



Fig. 271. — The muscles of the upper arm seen from the side and from behind. 

 The part of the antibrachial fascia which covers the anconeus has been removed and the outer head of the triceps 

 has been severed and turned aside in either direction. 



Fig. 272. — The muscles of the flexor surface of the upper arm, superficial layer. 

 The deltoid has been removed. 



Fig. 273. — The muscles of the flexor surface of the upper arm, deep layer. 

 The deltoid and biceps have been removed. 



Immediately below the coracoid process, and on the under surface of the subscapularis 

 near its insertion, there is a constant bursa which is a diverticulum of the synovial membrane of 

 the shoulder-joint and is known as the subscapular bursa (see page 121). 



The subscapularis is supplied by the subscapular nerves from the brachial plexus. It is an internal rotator of 

 the arm. 



THE MUSCLES OF THE UPPER ARM. 



THE MUSCLES OF THE FLEXOR SURFACE. 



Upon either side of the lower portion of the arm there is a distinct intermuscular septum 

 (Figs. 270 to 273) between the muscles of the flexor and those of the extensor surface. The 

 internal intermuscular septum is the stronger of the two and ends at the internal epicondyle, 

 the external intermuscular septum is weaker and extends downward as far as the external epicon- 

 dyle. These septa give origin to muscles of both groups, the external septum furnishing attach- 

 ment also for the radial group. 



The biceps (Figs. 272 and 273) is a long, large, spindle-shaped muscle which is situated 

 immediately beneath the brachial fascia in the anterior brachial and cubital regions, and arises 

 by two distinct heads, the long head and the short head. The long head arises from the supragle- 

 noidal tuberosity of the scapula by means of a long cylindrical tendon, which passes through 

 the cavity of the shoulder- joint (see page 121) and through the intertubercular groove, being 

 enveloped in the latter situation by the intertubercular mucous sheath (Fig. 273). The tendon 

 of the short head is short, flat, and adherent to that of the coracobrachialis; it comes from the 

 coracoid process of the scapula. 



Each head of the biceps forms a cylindrical muscular belly (the short head almost immedi- 

 ately after its origin) and the two bellies may remain separated for quite a distance, though in 

 immediate contact with one another, but always unite above the elbow-joint (never before reach- 

 ing the middle of the arm) to form a single muscle. The widest part of this muscle is at the 

 middle of the arm; and to cither side of it a distinct groove may be recognized, the internal 

 and external bicipital grooves. As it passes downward, the muscle becomes narrower, and in 

 the region of the elbow-joint it passes into a tendon of insertion which consists of two portions, 

 a deep, flat, strong tendon and a thin superficial portion known as the lacertus fibrosus (Figs. 

 272, 273, 274, and 291). The latter is composed of superficial radiating fibers from the tendon 



