Fig- 5-
H: Biceps, shows in both pronated and supinated positions and runs under the deltoid.
I: Brachialis anticus, dividing triceps and biceps.
J : Triceps, showing on side and back, and greatly forming the outline of the arm.
K: Supinator longus, being a muscle that reaches far up into the upper arm, moving with the radius bone and forming important outlines.
L : Extensor carpi radialis longior.
M : Flexor carpi radialis.
N : Extensor carpi radialis brevior.
0 : Extensor communis digitorum.
P : Extensor carpi ulnaris.
X : Extensor ossis metacarpi pollicis.
Supinator longus, in actual measurement, reaches one-third up the humerus, giving a short appearance to the upper arm.
The deltoid muscle reaches nearly half-way down humerus bone, and in outline a slight depression will be seen in the middle, the lower half having the most prominent curve (Figs. 7 and 9).