In the cat, the metacarpal bone of the thumb, although shorter than any of the others, is quite as thick. The third digit is a little longer than either the second or fourth. In animals of this genus, the claws, in the condition of repose, are retracted, and removed from the ground; this prevents their being worn, and thus preserves their sharpness. At such times the third phalanx is received into a groove which is found on the external surface of the second phalanx. In the dog, the claws are not tractile.
[Illustration: FIG. 37.--SKELETON OF THE FINGER OF A FELIDE (LION): LEFT SIDE, INTERNAL SURFACE.
1, Metacarpus; 2, sesamoid bones; 3, first phalanx; 4, second phalanx; 5, third phalanx; 6, gutter for the reception of the base of the nail; 7, prominent osseous crest formed to lodge in the concavity of the nail.]
[Illustration: FIG. 38.--SKELETON OF THE PIG: LEFT LATERAL SURFACE.
1, Cranium; 2, face; 3, atlas; 4, axis; 5, seventh cervical vertebra; 6, first dorsal vertebra; 7, fourteenth and last dorsal vertebra; 8, lumbar vertebræ; 9, sacrum; 10, coccygeal vertebræ; 11, anterior extremity of the sternum; 12, xiphoid appendix; 13, seventh and last sternal rib; 14, costal cartilage; 15, cartilage of prolongation of the scapula; 16, great tuberosity of the humerus; 17, olecranon process; 18, radius; 19, ulna; 20, pisiform; 21, metacarpus; 22, phalanges of the two great toes; 23, phalanges of the external toe; 24, ilium; 25, pubis; 26, tuberosity of the ischium; 27, great trochanter; 28, knee-cap; 29, anterior tuberosity of the tibia; 30, fibula; 31, tarsus; 32, calcaneum; 33, metatarsus; 34, phalanges of the two great toes; 35, phalanges of the external toe.]
=Unguligrades=: =Pig= (Fig. 38).--The scapula is markedly narrowed in the region above the glenoid cavity. The spine is atrophied at both its extremities, so that at its inferior part we do not find the acromion process. In its middle portion the spine is prominent, and presents a triangular process which turns backwards, overlapping a part of the infraspinous fossa; this latter is much larger than the supraspinous. The spinal border is surmounted by the cartilage of prolongation, the superior margin of which is convex; this cartilage extends posteriorly beyond the posterior (axillary) border of the bone.