The Arm
Arm: Bones and Muscles (Plate 10).
The onion shape is introduced as a guiding line for shape of arm (Fig. i). Blocking lines shown in Fig. 2, also Plate 11, Fig. 12.
A " pronated " arm is expressed when the thumb is turned towards trunk of body, and in appearance will be thick on the upper arm, tapering to wrist as in Fig. 3, also as in Plate 11, Fig. 11, the latter showing the pronation in bones, the radius crossing the ulna bone, which has been shaded to distinguish it.
In the supinated arm the thumb turns outwards, and will appear narrow across the upper arm and wide on lower arm (Fig. 4). This is caused by the upper arm being wider on the side than across the front, the reverse being the case in the lower arm.
When position is decided, block out as in Fig. 2 (also Plate 11, Fig. 12), placing elbow and wrist position at correct length on figure.
The side and outer view of arm bones is represented in Fig. 5. The bones are known by the following names
A : Humerus, upper arm bone.
B : Radius, used for turning the wrist.
C : Ulna, companion bone in lower arm.
Connecting with the arm bones are
D : Clavicle (collar bone). E : Scapula (shoulder blade).