Fig. 32.—Superior Limb of the Human Being, the Different Segments being placed in the Attitude which the Corresponding Parts occupy in Birds: Left Side, External Surface.
For the rest, in order to be able to distinguish readily the corresponding parts in the hand of a bird and that of a man, we merely have to place the human forearm obliquely, in a direction upwards and forwards ([Fig. 32]), the radius being above; this position we can obtain by semi-pronation; then, to incline strongly the hand downwards and backwards, moving the ulnar border of the hand towards the ulna; the thumb is then anterior, the little finger posterior, and the palm of the hand is turned towards the trunk.
The carpus in birds is formed by two bones only, with which the skeleton of the forearm articulates. That which is in contact with the radius is called the radial bone of the carpus; and that with which the ulna articulates is named the ulnar bone.
The metacarpus is formed of three bones; the first, which is very short, is fused at its superior extremity with the adjoining one; this latter and the third, both longer than the first, but of unequal size, are fused at their extremities. The metacarpal, which articulates with the radial bone of the carpus, is larger than the one which is in line with the ulna. To the metacarpus succeed three digits, of which the central is the longest, and is formed of two phalanges; the other two are formed each by a small, stylet-shaped bone. The middle finger, situated on the prolongation of the metacarpal, which articulates with the radial bone of the carpus, has its first phalanx large and flattened transversely; this phalanx seems to have been formed by the union of two bones of unequal development; the second phalanx is styloid in form. As to the other two fingers, they are placed, one in front and the other behind; the first, which articulates with the short metacarpal, fused at its upper end with the principal bone of the metacarpus, in position represents the thumb. The other, which is the third finger, articulates with the inferior extremity of the thinnest bone of the metacarpus; it is sometimes closely united to the corresponding border of the first phalanx of the large—that is to say, of the median—digit.
The Anterior Limbs in Certain Animals
Plantigrades: Bear ([Fig. 33]).—The scapula of the bear approaches in shape to a trapezium, of which the angles have been rounded off. The anterior border (cervical) is strongly convex in the part next the glenoid cavity. The junction of the superior (spinal) and the cervical border forms almost a right angle, the summit of which corresponds to the origin of the spine. At its posterior angle there is a prominence, directed downwards, the surface of which is hollowed and is separated from the infraspinous fossa by a crest, so that at this level a third fossa is added to the infraspinous one. The neck of the scapula is but slightly marked. The acromion is prominent, and projects a little beyond the glenoid cavity.
Fig. 33.—Skeleton of the Bear: Left Lateral Surface.