262 DISSECTION OF THE FRONT OF THE FOREARM. 



the ulnar nerve. The posterior branch continues along the back of the 

 forearm (ulnar side) to rather below the middle. 



The cutaneous part of the musculo-cutaneous nerve (p. 256) is pro- 

 longed on the radial border of the limb to the ball of the thumb, over 

 which it terminates in cutaneous offsets. Near the wrist the nerve is 

 placed over the radial artery, and some twigs pierce the fascia to ramify 

 on the vessel and supply the carpus. A little above the middle of the 

 forearm the nerve sends backwards a branch to the posterior aspect, which 

 reaches nearly to the wrist, and communicates with the radial, and the 

 following cutaneous nerve. 



The external cutaneous branch of the musculo-spiral nerve (p. 259) after 

 passing the elbow, turns to the hinder part of the forearm, and reaches as 

 far as the wrist. Near its termination it joins the preceding cutaneous 

 nerve. 



The radial nerve ramifies in the integument of the back of the hand 

 and some of the digits. It becomes cutaneous at the outer border of the 

 forearm in the lower third, and after giving some filaments to the poste- 

 rior aspect of the limb, divides into two branches : 



One (external) is joined by the musculo-cutaneous nerve, and is dis- 

 tributed on the radial border and the ball of the thumb. 



The other branch (internal) supplies the remaining side of the thumb, 

 both sides of the next two digits, and half the ring finger ; so that the 

 radial nerve distributes the same number of digital branches to the dorsum 

 as the median nerve furnishes to the palmar surface. This portion of the 

 radial nerve communicates with the musculo-cutaneous and ulnar nerves ; 

 and the offsets to the contiguous sides of the ring and middle fingers is 

 joined by a twig from the dorsal branch of the ulnar nerve. 



On the side of the fingers each of these dorsal digital branches is united 

 with an offset from the digital nerve on the palmar surface. 



The dorsal branch of the ulnar nerve gives offsets to the rest of the 

 fingers and the back of the hand. Appearing by the styloid process of the 

 ulnar, it joins the radial nerve in an arch across the back of the hand, and 

 is distributed to both sides of the little finger, and to the ulnar side of the 

 ring finger : it communicates with the part of the radial nerve supplying 

 the space between the ring and middle fingers. The ulnar nerve furnishes 

 branches to the same digits on the palmar surface. 



The aponeurosis of the forearm is continuous with a similar investment 

 of the arm. It is of a pearly white color, and is formed of fibres which 

 cross obliquely : it furnishes sheaths to the muscles, and is thicker behind 

 than before. 



Near the elbow it is stronger than towards the hand ; and at that part it 

 receives fibres from the tendons of the biceps and brachialis anticus, and 

 gives origin to the muscles attached to the inner condyle of the humerus. 

 On the back of the limb the aponeurosis is connected to the margins of the 

 ulna, so as to leave the upper part of the bone subcutaneous ; and it is 

 joined by fibres from the tendon of the triceps. 



Horizontal processes are sent downwards from the aponeurosis to sepa- 

 rate the superficial and deep layers of muscles, both on the front and back 

 of the forearm ; and longitudinal white bands indicate the position of the 

 intermuscular processes which isolate one muscle from another, and give 

 origin to the muscular fibres. 



At the wrist the fascia joins the anterior annular ligament ; and near 

 that band the tendon of the palmaris longus pierces it, and receives a sheath 



