168. The principal supinators arise from the external condyle of the humerus (fig. LXXX.), and are called long and short (fig. LXXX. 4, 5). The long supinator extends as far as the lower end of the radius, into which it is inserted (fig. LXXX. 4): the short supinator surrounds the upper part of the radius, and is attached to it in this situation (fig. LXXX. 5.). Moreover, the triceps, being inserted into the radius (164), often cooperates with the supinators and powerfully assists their action.
169. The principal pronators are also two, called the round and the square (figs. LXXXI. and LXXXVI. 1). The round pronator arises from the internal condyle, and passing downwards, is inserted into the middle of the radius (fig. LXXXI. 4); the square pronator is a small muscle between the radius and ulna, at their lower extremities being attached to each (fig. LXXXVI. 1).
View of the supinators of the radius and hand. 1. The
humerus; 2. the ulna; 3. the radius; 4. the muscle called
the long supinator passing to be inserted into the lower portion
of the radius; 5. the muscle, called the short supinator,
surrounding the upper part of the radius.
170. The action of these muscles in producing the rotation of the radius, and so rendering the hand supine or prone, is sufficiently manifest from the mere inspection of the diagrams (fig. LXXXI. 4).
View of the pronators of the hand. 1. Lower end of the
humerus; 2. the radius; 3. the ulna; 4. the muscle called
the round pronator, one of the powerful pronators of the hand.