208 MUSCLES OF THE UPPER LIMB. 



Nerves of the Brachial Muscles. — The three anterior flexor muscles are all 

 supplied from the musculo-cutaneous nerve : the brachialis anticus, hoM-ever, 

 receives also a small twig fi-om the muscialo-spiral nerve. The triceps and 

 anconeus receive their nerves entii'ely from the musculo-spiral. 



Actions. — The biceps muscle raises the arm at the shoulder and flexes the 

 elbow-joint ; the short head of the biceps draws the ann inwards as well as up- 

 wards, as does also the coraco-brachialis. If the biceps be called into action 

 when the hand is in pronation, its first effect, from its insertion into the back 

 part of the tuberosity of the radius, is to produce supination of the forearm. The 

 biceps also makes tense the fascia of the forearm. Tlie brachialis anticus is a 

 simple flexor of the elbow. The external and internal heads of the triceps and 

 the anconeus muscle, are simple extensors of the elbow joint ; the long head, 

 while it assists extension, also tends to depress the arm on the scapula. 



MUSCLES AND FASCLffi OF THE FOREAKM, 



Fascia. — The superficial fascia of the forearm is most distinct 

 opposite the bend of the elbow, where the superficial veins contained 

 within its laminse are numerous and large. In the palm of the hand, 

 on the contrary, the subcutaneous tissue forms a firm connecting 

 medium between the skin and a strong aponeurosis named the palmar 

 tascia : it consists of a network of fibres passing between those two 

 structures, dividing the subcutaneous fat into small granular masses, 

 and preventing the skin from shifting to any considerable extent. 



The aponeurosis of the for earm, like that of the arm, is composed 

 principally of circular fibres, strengthened, however, by longitudinal 

 and oblique fibres descending from the condylar eminences of the 

 humerus, fi'om the olecranon, and from the semilunar fascia of the 

 biceps muscle. It is attached along the subcutaneous margin of the 

 ulna, and may be conveniently divided into an anterior and a posterior 

 pai't. 



The anterior part of the aponeurosis of the forearm is much Aveaker 

 than the membrane on the posterior aspect of the limb. It is continued 

 below into the anterior annular ligament of the wrist. In the hollow im- 

 mediately below the bend of the elbow, it presents a small oval aperture 

 for the transmission of a short communicating branch between the super- 

 ficial and the deep veins of the forearm. It increases in density towards 

 the hand ; and a little above the wrist affords a sheath to the tendon of 

 the long palmar muscle, which passes over the annular ligament to be 

 inserted into the narrow end of the palmar fascia. Several white lines 

 seen on the surface of the fascia mark the positions of the septa between 

 the origins of the muscles descending from the inner condylar eminence, 

 which are continuous with it. Between the superficial and the deep 

 flexor muscles, another layer of fascia is stretched from side to side : it 

 is stronger below than above, where it generally consists of little more 

 than thin connective tissue. 



The anterior anmdar liijammt of the carpus, previously described at 

 p. 157, is continuous at its upper margin with the fascia of the forearm, 

 and receives some fibres from the tendon of the flexor carpi ulnaris: the 

 lower margin is connected with a deep part of the palmar fascia, and 

 gives origin in part to most of the short muscles of the thumb and 

 little finger. This structure may be considered in some measure as a 

 deep thickened ])ortion of the fascia of the wrist. 



Th& posterior portion of the aponeurosis of the forearm, much thicker 



