1202 SURFACE AND SURGICAL ANATOMY 
THE UPPER ARM. 
The anterior and posterior borders of the deltoid may be traced from the 
shoulder girdle to the insertion of that muscle. The surface relations of the anterior 
border have already been referred to; the posterior border forms a well-marked 
and important landmark as it crosses the angle between the axillary border of the 
scapula and the upper part of the shaft of the humerus. By making an incision 
along this part of the posterior border of the deltoid, and retracting the edge of the 
muscle upwards and outwards, we expose the surgical neck of the humerus, the 
quadrilateral opening in the posterior wall of the axilla transmitting the posterior 
circumflex artery and the circumflex nerve; a little lower down is the musculo- 
spiral nerve. The coraco-brachialis, the guide to the upper half of the brachial 
artery, forms a prominence occupying the upper half of the indernal bicipital furrow. 
Traced downwards the internal bicipital furrow widens out into an elongated 
triangle. This triangle, which may be termed the internal supracondyloid triangle, 
Head of radius Extensor carpi radialis brevior 
External condyle Posterior interosseous nerve 
Extensor carpi radialis longior | Extensor ossis metacarpi pollicis 
Musculo-spiral nerve | Middle theeal tubercle 
External intermuscular septum Biceps | Styloid process of 
Circwnflex nerve \ | third metacarpal 
Jud | | 
ll cere mi i 
a | ale ill ) 
« | A + f 
lL eeescertirtt se iil y 
lf i 
iy) We, 
| 
ij M Head of ulna 
nn Wid 
one Posterior border of ulna 
1 | Flexor carpi ulnaris 
| 
AN Wf Hs lll ii 
| ie sida 
i 
Triceps tendon 
Outer head of triceps 
Extensor carpi ulnaris 
| Extensor communis digitorum 
| 
ra i ( 
\ Posterior border of deltoid |  Anconens 
\ Long head of triceps Tip of olecranon process 
Teres major 
Infraspinatus Latissimus dorsi 
Fic. 810.—ExtTensor ASPECT OF Upper LIne. 
becomes continuous below with the inner part of the triangle in front of the bend 
of the elbow, and is limited posteriorly by the internal intermuscular septum, which 
may be felt as a cord-hke band extending upwards from the internal condyle; the 
floor of the space is formed by the inner part of the brachialis anticus. Within 
the triangle are the following nnportant structures, enumerated from without in- 
wards, viz.: the brachial artery, the median nerve, the lower part of the basilic 
vein, the internal cutaneous nerve, and the supracondyloid lymphatic glands, two 
or three in number. Extending upwards from the external condyle to the insertion 
of the deltoid is the external intermuscular septum, which is pierced at the 
junction of its upper and middle thirds by the musculo-spiral nerve. Between the 
external intermuscular septum and the outer edge of the biceps is the ill-defined 
eaternal bicipital furrow, the floor of which is formed by a strip of the brachialis 
anticus, and, nearer the elbow, by the supinator longus and extensor carpi radialis 
longior. 
The posterior compartment of the upper arm is occupied by the triceps, the Jong 
head of which can be traced upwards to the axillary border of the scapula in front 
of the posterior border of the deltoid and behind the posterior fold of the axilla. 
The outer head of the triceps, after emerging from under cover of the lower part 
of the posterior border of the deltoid, is continued ol liquely down the outer aspect 
of the upper arm as a well-marked muscular elevation. Above the olecranon - As. 
the strap-hke tendon of insertion of the triceps, which, when the elbow is fully 
flexed, forms an admirable posterior splint in supracondyloid fractures of the 
humerus. 
The brachial artery, slightly overlapped in the upper half of the arm by the 
coraco-brachialis and in the lower half by the biceps, ean be felt pulsating through- 
out the whole length of the anterior part of the internal bicipital furrow. The 
