THE ARM 



1415 



In ligature of the artery here the line extends from the mid-axillary region above, prolonged 

 to the centre of the front of the elbow. The only structures seen should be the medial 

 edge of the biceps, the basilic vein, and the median nerve. The profunda comes off 2.5 cm. 

 (1 in.) below the teres major, having the same relation to the heads of the triceps; thus, it first 

 lies on the long head, behind the axillary and brachial arteries, then between the long and 

 medial heads, and next, in the groove, between the medial and lateral heads, and courses with 

 the radial (musculo-spiral) nerve (fig. 1132); the nutrient artery arises opposite the middle 

 of the humerus; in many cases it arises, on the back of the arm, from the profunda; the superior 

 ulnar collateral (inferior profunda) below the middle, and courses with the ulnar nerve through 

 the intermuscular septum to the back of the medial condyle. The inferior ulnar collateral 

 (anastomotica magna) is given off from 2.5 to 5 cm. (1 to 2 in.) above the bend of the elbow. 

 Fig. 1138 will show the collateral circulation after ligature of the brachial, according as the 

 vessel is tied above or below the superior profunda, or below the superior ulnar collateral. 



The centre of the arm is a landmark for many anatomical structures. On the 

 lateral side is the insertion of the deltoid; on the medial, that of the coraco- 

 brachialis. The basilic vein and the medial brachial cutaneous nerve (nerve of 

 Wrisberg) here perforate the deep fascia, going in reverse directions. The supe- 

 rior ulnar collateral is here given off from the brachial and joins the ulnar nerve; 

 the median nerve also crosses the artery, and the ulnar nerve leaves the medial 

 side of the vessel to pass to the medial aspect of the limb. 



The brachialis can be mapped out by two pointed processes which surround the insertion 

 of the deltoid, pass downward into lines corresponding to the two intermuscular septa, and then 

 converge over the front of the elbow to their insertion into the coronoid process. 



The median nerve (lateral head, 5th. 6th, 7th C; medial head, 8th C. and 1st T.) can be 

 traced by a line drawn from the lateral side of the third part of the axillary and first part of the 

 brachial artery, across this latter vessel about its centre, and then along its medial border to 

 the forearm, where it passes between the two heads of the pronator teres. 



Fig. 1133. — Cross-Section through the Elbow. (X 1/2). (After Braune.) 



Tendon of biceps- 



Brachio-radialis 



Radial nerve 



Brachialis. 



Extensor carpi radialis longus- 



Anconeus— - 



Pronator teres 

 Median nerve 



Flexor carpi radialis 



•Ulnar collateral ligament 

 Ulnar nerve 

 •Olecranon 



Tendon of triceps 



The ulnar nerve (8th C. and 1st T.) lies to the medial side of the above arteries as far as 

 the middle of the arm, where it leaves the brachial to course more medially and perforate the 

 medial intermuscular septum together with the superior and posterior branch of the inferior 

 ulnar collateral and so get to the back of the medial condyle. A line drawn from the medial 

 border of the coraco-brachialis, where, in the upper part of its course, the nerve is in close rela- 

 tion with the medial side of the axillary and brachial arteries, to the back of the medial condyle , 

 will indicate its course. Low down, the nerve is in the medial head of the triceps, and may be 

 injured in operations here. 



The radial (musculo-spiral) nerve (5th, 6th, 7th, and 8th C.) can be traced by a line begin- 

 ning behind the third part of the axillary artery, then carried vertically down behind the upper- 

 most part of the brachial, and then, just below the posterior border of the axilla, curving back- 

 ward behind the humerus and slightly downward just below the insertion of the deltoid. Thus, 

 passing from laterally and from before backward in its groove, accompanied by the profunda 

 vessels, first the trunk, and then the smaller anterior division, it again comes to the front by 

 perforating the lateral intermuscular septum at a point about opposite to the junction of the 

 middle and lower thirds of the arm, and passes down in front of the lateral supracondyloid 

 ridge, lying here between the brachio-radialis and brachialis anterior, to the level of the lateral 

 condyle, in front of which it divides into the superficial (radial) and deep (posterior interos- 

 seous) radials. The former of these accompanies the radial artery to the front of the arm, the 

 latter travels backward to the back of the forearm. A line from the lateral condyle to the 

 insertion of the deltoid indicates the lateral intermuscular septum. 



In addition to injuries caused by fracture, the nerve may be injured in crutch pressure, 

 the sleep of intoxication, use of an Esmarch's bandage, or the careless reduction of a dislocated 

 shoulder with the foot in the axilla. To expose the nerve the incision begins below, over the 

 lateral intermuscular septum, where it lies between the brachio-radialis and brachialis (anterior). 

 Hence the incision is prolonged freely upward and backward toward the posterior border of the 

 deltoid. 



On the back of the arm is the triceps muscle, with its three heads and tendon 

 of insertion, all brought into relief in a muscular subject when the forearm is 

 strongly extended. Of the three heads, the medial is the least distinct, arising 



