FIG. 74.—FLAT BONE (Scapula).
The Human frame consists of a skeleton (fig. 73) formed of hard and unyielding bone, having joints to admit of motion in certain directions; this skeleton performs certain great and important offices, it forms strong boundaries or protecting cases for most of the vital parts, so as to shield them from external violence, such as the brain and spinal cord, the lungs, heart, &c., it also furnishes a series of levers to be acted on by the muscles, for the purposes of motion, and a firm support for the soft parts of the system. The skeleton is divided into the head, trunk, and extremities; the head is again divided into cranium and face; the trunk is divided into spine, thorax, and pelvis; the extremities into the upper and lower, the upper consisting of arm, fore-arm, and hand; the lower of thigh, leg, and foot. The bones are divided into "flat bones" (fig. 74) and "long bones" (fig. 75), the flat bones (as a general rule) form the boundaries of the cavities, and the long bones the levers.
FIG. 75.—LONG BONE (Femur).
FIG. 76.—SECTION OF BONE, MAGNIFIED.
FIG. 77.—FIBRILS OF VOLUNTARY MUSCLE, MAGNIFIED.
FIG. 78.—THE SAME, MORE HIGHLY MAGNIFIED.