. Applied anatomy and kinesiology. Fig. 126.—Position of the lungs in the chest. (Gerrish.) rotation of each rib on the axis passing through its two the resting position the ribs slant downward at an angle of 15 to20 degrees from the horizontal, and, as a consequence, their eleva-tion carries the sternum and the whole front of the chest awayfrom the spinal column, as shown in Fig. 127. This enlarges thechest from front to rear; since the ribs slant downward and side-ward where they join the spinal column, their elevation will increasethe lateral diameter of the chest as well. In
. Applied anatomy and kinesiology. Fig. 126.—Position of the lungs in the chest. (Gerrish.) rotation of each rib on the axis passing through its two the resting position the ribs slant downward at an angle of 15 to20 degrees from the horizontal, and, as a consequence, their eleva-tion carries the sternum and the whole front of the chest awayfrom the spinal column, as shown in Fig. 127. This enlarges thechest from front to rear; since the ribs slant downward and side-ward where they join the spinal column, their elevation will increasethe lateral diameter of the chest as well. In order to expand thechest, therefore, there must be muscular action that will lift the 210 BREATHING The muscles acting to raise the ribs in quiet normal breathingare the external intercoslals, the diaphragm, and probably theinternal Fig. 127.—Enlargement of the chest by elevation of the ribs. (Gerrish.) EXTERNAL INTERCOSTALS. Eleven sheets of muscular fibers located in the spaces betweenthe ribs (Fig. 128). Origin.—^The lower borders of the first eleven ribs. Insertion.—^The upper borders of the last eleven ribs. Structure.—Short parallel fibers extending diagonally forwardand downward, in the direction of the external oblique. It extendsfrom the spinal column forward to the costal cartilages, beingabsent next to the sternum. Action.—The pull is evidently calculated to draw the ribs closertogether. Duchenne reports that stimulation of the external inter-costal muscles causes a lift of the rib below, without depressingthe rib above. Although the action has been in dispute it is nowgenerally agreed that the external intercostals act to lift the ribsin inspiration. INTERNAL INTERCOSTALS. Eleven muscular sheets just beneath the external intercostals. Structure.—Fibers extending downward and backward, like
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