DISSECTION OF THE FOREARM. 



Branches. 



Internal 



cutaneous 



branch. 



Two exter- 

 nal cuta- 

 neous. 



Branches to 

 the triceps, 



ulnar 

 collateral 

 and an- 

 coneus, 



brachialis 

 anticus and 

 muscles of 

 forearm. 



Directions. 



posterior interosseous nerves (fig. 37, 2 and 3 ). The brachialis anticus 

 and supinator longus muscles are sometimes partly blended, and it 

 may be necessary in such cases to cut through some muscular fibres 

 to fully expose the last part of the nerve. The nerve gives 

 muscular branches and cutaneous offsets to the inner and outer 

 sides of the limb. 



a. The internal cutaneous branch of the arm (fig. 20, 6 also fig. 15, 

 p. 39) is of small size, and arises in the axillary space in common 

 with the branch to the inner head of the triceps ; it is directed across 

 the posterior boundary of the axilla to the inner side of the arm, 

 where it becomes cutaneous in the upper third, and is distributed as 

 before said (p. 43). 



b. The external cutaneous branches, springing at the outer side of 

 the limb, are two in number ; they are distributed in the integuments 

 of the arm and forearm (pp. 42 and 57). 



c. The muscular branches to the triceps are numerous, and supply 

 all three heads. One slender offset (often called the ulnar collateral 

 branch) for the inner head arises in common with the internal 

 cutaneous branch, and descends close to the ulnar nerve to enter the 

 muscular fibres at the lower third of the arm. Another long and 

 slender branch behind the humerns, appearing as if it ended in the 

 triceps, can be followed downwards to the anconeus muscle. 



d. On the outer side of the limb the musculo-spiral nerve supplies 

 the brachialis anticus in part, and two muscles of the forearm, viz., 

 supinator longus and extensor carpi radialis longior. 



Directions. As the dissection of the arm has been completed as 

 far as the elbow, it will be advisable to keep moist the shoulder- 

 joint until it is examined with the other ligaments. 



SECTION IV. 



Position of 

 the limb. 



Surface of 

 the forearm 



Bony pro- 

 jections. 



Line of the 

 wrist-joint. 



THE FRONT OF THE FOREARM. 



Position. The limb is to be placed with the palm of the hand 

 uppermost ; and the marking of the surface and the projections of 

 bone are first to be noted. 



Surface-marking. On the anterior aspect of the forearm are two 

 lateral depressions, corresponding with the position of the main 

 vessels. The external is placed over the radial artery, and inclines 

 towards the middle of the limb as it approaches the elbow. The 

 internal groove is evident only below the middle of the forearm, 

 and points out the place of the ulnar artery. 



The bones (radius and ulna) are sufficiently near the surface to 

 be traced in their whole length : each ends below in a point on 

 either side of the wrist the styloid process ; and that of the radius 

 is the lower. A transverse line separates the forearm from the 

 hand, and the articulation of the wrist is about three-quarters of an 

 inch above it. 



