THE MUSCLES OF THE ARM 303 
Structure—The peculiar spiral course of this muscle gave rise to the name 
often applied to it—humeralis obliquus. Beginning on the posterior surface of the 
shaft, close to the head of the humerus, it winds over the lateral surface, crosses the 
biceps very obliquely, and finally reaches the medial side of the forearm by passing 
between the biceps and the extensor carpi. It is entirely fleshy, with the exception 
of its relatively slender tendon of insertion. Some fibers at the proximal end are 
attached to the capsule of the shoulder joint, which may thereby be tensed during 
flexion. 
Relations.—Laterally, the skin and fascia, the teres minor, deltoid, triceps 
(lateral head), and brachiocephalicus muscles. Deeply, the teres major, the bi- 
ceps, and the humerus. The anterior radial artery crosses the deep face of the 
muscle in its distal third, and the radial nerve accompanies the muscle in the distal 
half of the musculo-spiral groove. 
Blood-supply.—Brachial artery. 
Nerve-supply—Musculo-cutaneous nerve; frequently radial nerve also. 
3. Tensor fascia antibrachii (Fig. 277)..—This is a thin muscle which lies 
chiefly on the medial surface of the triceps. 
Origin.—The tendon of insertion of the latissimus dorsi and the posterior 
border of the scapula. 
Insertion —(1) The deep fascia of the forearm; (2) the olecranon. 
Action.—(1) To tense the fascia of the forearm and to extend the elbow joint. 
Structure —The origin consists of a very thin aponeurosis which blends with 
those of the caput longum and the latissimus dorsi. In most cases there is a dis- 
tinct division into anterior and posterior heads. The muscular portion is thin in 
its anterior part, somewhat thicker behind, and is narrower than the aponeurotic 
origin. It is succeeded by an aponeurotic insertion, which ends chiefly by blending 
with the fascia of the forearm a little below the elbow. There is, however, a small 
but constant tendinous attachment to the olecranon. 
Relations.—Laterally, the cutaneus, triceps (long and medial heads), the medial 
and middle flexors of the carpus, and the ulnar vessels and nerve; medially, the 
latissimus dorsi, serratus ventralis, and posterior pectoral muscles. 
Blood-supply.—Subscapular, ulnar, and deep brachial arteries. 
Nerve-supply.—Radial nerve. 
4. Triceps brachii (Figs. 267, 268, 277).—This, together with the preceding 
muscle, constitutes the large muscular mass which fills the angle between the pos- 
terior border of the scapula and the humerus. It is clearly divisible into three 
heads. 
(a) Long head (Caput longum tricipitis).~—This, the largest and longest of 
the three heads, is a powerful, thick, triangular muscle, which extends from the 
posterior border of the scapula to the olecranon. 
Origin.—The posterior border of the scapula. 
Insertion —The lateral and posterior part of the summit of the olecranon. 
Action—(1) To extend the elbow joint; (2) to flex the shoulder joint. 
Structwre—The muscle arises by a wide, strong aponeurosis from the posterior 
border of the scapula. From this the bundles of the fleshy portion converge to 
the short, strong tendon of insertion. A careful examination will show that the 
muscle is penetrated by a tendinous intersection from which many fibers take origin 
obliquely. The superficial face is covered by an aponeurosis which is specially 
developed at its distal part. A small bursa occurs under the tendon of insertion. 
‘M’Fadyean and Vaughan term this muscle the scapulo-ulnaris, while Arloing and Lesbre 
term it ‘‘Anconé accessoire du grand dorsal.’ The above name seems to agree best with the 
chief insertion and action, although it certainly arises largely from the tendon of insertion of the 
latissimus dorsi. 
* Also known as the anconzeus longus or caput magnum. 
