Outlines of human physiology . six lower true ribs admit of the same kind ofmotion upon their vertebral joints, and contribute toraise and carry forward the middle and lower part ofthe sternum for the same purpose. By this provision, all the muscles of the trunk, thelower attachment of which is to the ribs, are renderedcapable of increasing the depth of the chest, or its dia-meter from before backwards ; and the opposite class ofmuscles, of diminishing the area of the chest in thesame dimensions. .11 the ribs, but the first, admit of a limited degreeof rotation upon their verte-bral
Outlines of human physiology . six lower true ribs admit of the same kind ofmotion upon their vertebral joints, and contribute toraise and carry forward the middle and lower part ofthe sternum for the same purpose. By this provision, all the muscles of the trunk, thelower attachment of which is to the ribs, are renderedcapable of increasing the depth of the chest, or its dia-meter from before backwards ; and the opposite class ofmuscles, of diminishing the area of the chest in thesame dimensions. .11 the ribs, but the first, admit of a limited degreeof rotation upon their verte-bral and sternal marks, even in thefcetal state, the limited de-gree of motion, which the firstrib is intended to enjoy, byforming its cartilage of onepiece with the sternum, towhich the cartilages of thesucceeding ribs are alreadyarticulated by moveablejoints J and by disposing allits parts in one plane. If anoblique plane were imaginedto pass through each articu-lar surface of any pair ofribs between the second and. 58 Mechanism by which the Chest admits of tenth inclusively, great part of the shaft and cartilage ofthese ribs would fall below it. If the intermediate partof these ribs be raised towards the imaginary planeby the rotation of each upon its sternal and vertebraljoints, it is obvious that the transverse diameter of thechest becomes increased. The advantage derived fromthe motion of the ribs on both their articular extremi-ties is intended to be explained by the adjoined figure. By this provision the same muscles, which contributeto enlarge the depth of the thorax, are rendered capa-ble of adding to its breadth, and the same which dimi-nish its area in the first dimension, are fitted to dimi-nish it in the second. The chest is closed above, by a fascia or layer ofcondensed cellular membrane, which extends acrossfrom the spine to the sternum, from the first rib of oneside to the opposite, and is perforated by the windpipe,by the oeso-phagus, by nerves, and
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Keywords: ., bookcentury1800, bookidoutlinesofhumanp00, booksubjectphysiology
