50 



DISSECTION OF THE ARM. 



Musculo- 

 cutaneous 

 nerve in the 



its muscular 

 branches. 



Dissection. 



Define 

 brachialis. 



Brachialis 

 anticus : 

 origin ; 



insertion ; 



relations of 

 surfaces, 



of borders ; 



use, fore- 

 arm free, 



and fixed. 



The MUSCULO-CUTANEOUS NERVE, named from supplying muscles 

 and integuments, ends on the surface of the forearm. It leaves the 

 outer cord of the brachial plexus opposite the lower border of the 

 pectoralis minor, and immediately perforates the coraco-brachialis ; 

 it is then directed obliquely to the outer side of the limb beneath 

 the biceps and lying upon the brachialis anticus. At the front of 

 the elbow it becomes a cutaneous nerve of the forearm. 



Branches. The nerve furnishes a branch to the coraco-brachialis 

 before entering the muscle, arid others to the biceps and brachialis 

 anticus where it is placed between them. 



Dissection. The brachialis anticus muscle will now be brought 

 into view by cutting through the tendon of the biceps near the 

 elbow, and turning upwards this muscle. The fascia and areolar 

 tissue should be taken from the fleshy fibres ; and the lateral extent 

 of the muscle should be denned on each side, so as to show that it 

 reaches the internmscular septum largely on the inner side, but 

 only for a short distance above on the outer side. 



Some care is required in detaching the brachialis on the outer 

 side from the muscles of the forearm, to which it is closely applied. 

 As the muscles are separated, the musculo-spiral nerve, accompanied 

 by a small branch of the superior profunda artery, comes into sight. 



The BRACHIALIS ANTICUS (fig. 20, H) covers the elbow-joint and 

 the lower half of the front of the humerus. It arises from the 

 anterior surface of the humerus below the insertion of the deltoid 

 muscle, and from the interamscular septa on the sides, viz., from 

 all the inner, but from only the upper part of the outer (fig. 17, 

 p. 44). The fleshy fibres converge to a tendon, which is inserted 

 into the impression on the front of the coronoid process of the 

 ulna (fig. 25, p. 61). 



This muscle is for the most part concealed by the biceps. On it 

 lie the brachial vessels, with the median, musculo-cutaneous, and 

 musculo-spiral nerves. It covers the humerus and the articulation 

 of the elbow. Its origin embraces by two slips the tendon of the 

 deltoid ; and its insertion is placed between two fleshy points of the 

 flexor profundus digitorum. The inner border reaches the inter- 

 muscular septum in all its length ; but the outer is separated below 

 from the external intermuscular septum by two muscles of the 

 forearm, supinator longus and extensor carpi radialis longior. 



Action. The brachialis brings forward the ulna towards the 

 humerus, and bends the elbow-joint. 



If the ulna is fixed, as in climbing with the hands above the 

 head, the muscle bends the joint by raising the humerus. 



Position of 

 the part. 



BACK OF THE ARM. 



Position. During the examination of the back of the arm, the 

 limb is to be raised in a semiflexed position by means of a block 

 beneath the elbow. The scapula is to be brought nearly in a line 

 with the humerus, so as to tighten the muscular fibres ; and it is to 

 be fastened with hooks in that position. 



