Fig. 28.—Inferior Extremity of the Bones of the Forearm of a Man: Left Side, Posterior Surface, Position of Supination.
1, Radius; 2, ulna; A, groove for the long abductor and short extensor muscles of the thumb; B, groove for the radial muscles; C, groove for the long extensor of the thumb; D, groove for the special extensor of the index finger and of the common extensor of the fingers; E, groove for the proper extensor of the little finger; F, groove for the posterior ulna.
In animals, because of the movement of rotation of the radius, the surface of this bone, which is anterior, corresponds to the posterior surface of the same in man. (To possess a clear conception of this, it is necessary to remember that, in this latter, the bones of the forearm are always described as in the position of supination; they are thus represented in [Fig. 28]. The direction of the surfaces of the radius is the reverse of that in animals, since the latter have the radius always in a state of pronation.)
Fig. 29.—Inferior Extremity of the Bones of the Forearm of the Dog: Left Side, Anterior Surface, Normal Position—that is, the Position of Pronation.
1, Radius; 2, ulna; A, groove for the long abductor and for the short extensor of the thumb; B, groove for the radials; D, groove for the long extensor of the thumb, the special extensor of the index-finger, and the common extensor of the fingers; E, groove for the special extensor of the little finger.
Consequently it is on the anterior surface of the bone that we find the grooves concerning which it is necessary to give some details. Regarding them in passing from the radius towards the ulna, those grooves give passage to the tendons of the muscles whose names occupy the columns on [p. 43]. The letters which are referred to each serve to define their order, and to facilitate reference to [Figs. 28], [29], and [30].