78 THE UPPER EXTREMITY 



Nervus Musculocutaneus. The musculo-cutaneous nerve 

 arises from the lateral cord of the brachial plexus, at the 

 lower border of the pectoralis minor. Inclining laterally, 

 it perforates the coraco-brachialis, and appears between the 

 biceps brachii and the brachialis. It proceeds obliquely 

 distally between these muscles until it reaches the bend 

 of the elbow, where it comes to the surface at the lateral 

 border of the tendon of the biceps brachii. From this 

 point onwards it has already been traced as the lateral 

 cutaneous nerve of the forearm (p. 67). 



In the upper arm the musculo-cutaneous supplies branches 

 to the three muscles in this region. The branch to the 

 coraco-brachialis is given off before the parent trunk enters 

 the substance of the muscle ; the branches to the biceps 

 brachii and brachialis issue from it as it lies between them. 



M. Coracobrachialis. This is an elongated muscle, which 

 takes origin from the tip of the coracoid process in con- 

 junction with the short head of the biceps brachii. It pro- 

 ceeds distally, along the medial margin of the biceps brachii, 

 and obtains insertion into a linear ridge situated upon the 

 medial aspect of the body of the humerus about its middle. 



M. Biceps Brachii (O.T. Biceps). The biceps brachii 

 muscle arises from the scapula by two distinct heads of origin. 

 The short or medial head springs from the tip of the coracoid 

 process in conjunction with the coraco-brachialis (Fig. 15, 

 p. 34). The long or lateral head is a rounded tendon, which 

 occupies the intertubercular sulcus of the humerus. Its 

 origin cannot be studied at this stage of the dissection 

 because it is placed within the capsule of the shoulder-joint. 

 Suffice it for the present to say, that it arises from an im- 

 pression on the scapula immediately above the glenoid cavity. 

 Both heads swell out into elongated fleshy bellies, which, at 

 first, are closely applied to each other, and afterwards united 

 in the lower third of the arm. Towards the bend of the 

 elbow the fleshy fibres converge upon a stout, short tendon, 

 which is inserted into the dorsal part of the tuberosity of 

 the radius. This insertion will be more fully examined at a 

 later period, but it may be noticed in the meantime that the 

 tendon is twisted so as to present its margins to the front 

 and dorsal aspect of the limb, and further, that a bursa 

 mucosa is interposed between it and the volar smooth part 

 of the radial tuberosity. 



