Fig. 8.—Anterior Limb of the Bat: Left Side, Anterior Surface.
1, Clavicle; 2, scapula; 3, humerus; 4, radius; 5, cubitus; 6, carpus; 7, thumb; 8, metacarpus; 9, phalanges.
They constitute the forepaw in terrestrial mammals; in aerial vertebrates they form wings; in aqueous mammals they act as paddles. In whatever series we study them, we can readily find the relationship of the different parts; it is very easy to recognise the same bones in the upper limbs of the human being, the wings of the bat ([Fig. 8]) and of birds ([Fig. 21]), and in the anterior paddles of the seal ([Fig. 9]) and of the dolphin.
Fig. 9.—Anterior Limb of the Seal: Left Side, External Surface.
1, Scapula; 2, humerus; 3, radius; 4, ulna; 5, carpus; 6, metacarpus; 7, phalanges of the fingers.
In quadrupeds, the shoulder and arm are hidden, the latter more or less completely, in the muscular mass which binds it to the lateral wall of the trunk; so that the anterior limbs only present; free from the trunk: the elbow, forearm, and hand.
The Shoulder
In some vertebrates, the shoulder is formed of two bones—the scapula and clavicle; in others of only one bone—the scapula; the clavicle in this case does not exist.