. Elements of human physiology. Physiology. chest-wall, leaving the vertebral and costal attachments intact, contraction of these muscles will cause a rise of both ribs. This result will be evident from a consideration of Fig. 189, where a i is a fibre of the external intercostal muscles, passing from the rib u s to be attached to the rib v' s' at b. When a b contracts, the tension it exerts on its two attachments can be resolved into two components a c acting downwards and b d acting upwards, b d however acts at the end of the long lever b v', whereas a c acts at the end of a short Fig.
. Elements of human physiology. Physiology. chest-wall, leaving the vertebral and costal attachments intact, contraction of these muscles will cause a rise of both ribs. This result will be evident from a consideration of Fig. 189, where a i is a fibre of the external intercostal muscles, passing from the rib u s to be attached to the rib v' s' at b. When a b contracts, the tension it exerts on its two attachments can be resolved into two components a c acting downwards and b d acting upwards, b d however acts at the end of the long lever b v', whereas a c acts at the end of a short Fig. lever a v. Hence the raising effect will overcome the depressing effect, and both ribs will rise. The fibres of the internal intercostals run in the opposite direction to the external nuiscles, and from a consideration of Fig. 190 it is evident that their effect will be to depress any pair of ribs, thus acting as expiratory muscles. Owing to the fact that the costal cartilages make an angle with the bony ribs, the fibres of prolongation of the internal intercostals, mtiscitli intcrcarti- laginei, have the same relation to their attachments that the external inter- costals have to the bony ribs. Their action therefore must be to raise the. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Starling, Ernest Henry, 1866-1927. Chicago : W. T. Keener
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