150 THE NERVOUS SYSTEM 



All these muscles arise from a common origin on the medial epicondyle 

 of the humerus. The Pronator Teres passes distally and laterally to be 

 inserted into the middle of the lateral aspect of the radius. It acts 

 as a powerful pronator and as a weak flexor of the forearm. It can 

 be recognised since it forms the medial boundary of the depression which 

 appears in front of the elbow, when the pronated forearm is flexed against 

 resistance. 



The Flexor Carpi Radialis passes somewhat obliquely through the 

 forearm and is inserted into the bases of the second and third metacarpal 

 bones. Its tendon is rendered prominent just proximal to the wrist, 

 when the joint is actively flexed ; it lies about half an inch to the lateral 

 side of the middle line. This muscle bears the same relation to radial 

 deviation of the hand as the flexor carpi ulnaris bears to ulnar deviation 



(P- 145)- 



The Palmaris Longus is absent in about 10 per cent, of subjects. It 

 is inserted into the palmar aponeurosis, and its tendon can be distinguished 

 to the medial side of the flexor carpi radialis tendon, when the wrist-joint 

 is actively flexed. 



The Flexor Digitorum Sublimis is partly overlapped by the three 

 preceding muscles. It breaks up into four tendons, which are inserted 

 into the second phalanges of the medial four digits. When the fist is 

 tightly clenched, with the wrist extended, a slight hollow appears on 

 the medial side of the palmaris longus tendon, and in the floor of this 

 depression the tendons for the ring and little fingers can be felt. 



The median nerve passes distally through the forearm, 

 deep to the superficial group of muscles. Just distal to the 

 elbow-joint, it gives off the volar interosseous nerve, which 

 descends on the interosseous membrane and supplies the 

 deep muscles of the front of the forearm, namely, the flexor 

 pollicis longus, the pronator quadratus and the radial half of 

 the flexor digitorum profundus. 



The Flexor Pollicis Longus arises from the anterior aspect of the 

 radius and is inserted into the distal phalanx of the thumb. Its tendon 

 is overlapped by the tendon of the flexor carpi radialis and is consequently 

 difficult to feel, but, if the fist is tightly clenched, a visible depression 

 appears on the radial side of the flexor carpi radialis tendon when the 

 flexor pollicis longus is contracted. 



The Pronator Quadratus arises from the distal part of the volar surface 

 of the ulna and is inserted into a corresponding area on the radius. It 

 is very deeply placed and its contractions cannot be appreciated either by 

 inspection or by palpation. 



