58 



DISSECTION OF FRONT OF FOREARM. 



which 

 supply 

 digits ; 



and branch 

 of ulnar 

 nerve to 

 back of 

 hand and 

 fingers. 



Extent of 

 nerves on 

 fingers. 



Deep fascia 

 of forearm : 



at the 

 wrist ; 



posterior 



annular 



ligament. 



Take away 

 fascia, 

 nerves, and 

 veins. 



Clean out 

 hollow of 

 elbow. 



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 offset to the con- 

 tiguous sides of the ring and middle fingers is joined by a twig from 

 the dorsal branch of the ulnar nerve. 



The DORSAL BRANCH OF THE ULNAR NERVE (fig. 23) gives offsets 



to the rest of the fingers and the back of the hand. Appearing by the 

 styloid process of the ulna, 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 furnished to the space between 

 the ring and middle fingers ; and sometimes it supplies this space 

 entirely. 



The dorsal digital nerves are much smaller than those on the 

 palmar aspect, and cannot be followed on the fingers farther than 

 the base of the second phalanx. On the sides of the finger each 

 communicates with an offset from the palmar nerve. 



The APONEUROSIS of the forearm is continuous with the similar 

 investment of the arm. It is of a pearly white colour, and is formed 

 of fibres which cross obliquely. The membrane is thicker behind 

 than in front, and is stronger near the elbow than towards the wrist. 

 At the upper part it receives prolongations from the tendon of the 

 biceps in front, and of the triceps behind ; and it gives origin to 

 the muscles springing from the condyles of the humerus. Longi- 

 tudinal white lines indicate the position of deep processes (inter- 

 muscular septa), which separate the muscles, and give origin to 

 their fleshy fibres. On the back of the forearm the fascia is 

 attached to the hinder border of the ulna, and to the margins of a 

 triangular surface at the upper end of that bone, which is left 

 subcutaneous. 



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 from it. Close to the pisiform bone there is an 

 aperture through which the ulnar vessels and nerve enter the fat of 

 the hand. Behind the wrist it is thickened by transverse fibres, 

 giving rise to the posterior annular ligament ; but on the back 

 of the hand and fingers the fascia becomes very thin. 



Dissection. The skin is now to be replaced on the back of the 

 forearm and hand, in order that the denuded parts may not become 

 dry. Beginning the dissection on the anterior surface of the limb, 

 let the student divide the aponeurosis as far as the wrist, and take 

 it away with the cutaneous vessels and nerves, except the small 

 palmar cutaneous offsets of the median and ulnar nerves near the 

 hand. In cleaning the muscles it will be impossible to remove the 

 aponeurosis from them at the upper part of the forearm without 

 cutting the muscular fibres. 



In front of the elbow is the hollow, already partly dissected, 

 between the two masses of muscles arising from the inner and outer 



