. A text-book of human physiology . these muscles are pres-ent only for the purpose of regulatingthe tension in the intercostal spacesand of rotating the thorax in its longaxis. By observations on living animalsin which all the muscles of respirationwere excluded except the intercostals,it has now been made clear that the outer layer, as well as that part of the inner included between the costal carti-lages, serves to elevate the ribs, while the remainder of the inner layer drawsthe ribs down (Bergendal and Bergman, E,. Du Bois-Reymond and ^lasoin, ). In the rabbit at least the intercost
. A text-book of human physiology . these muscles are pres-ent only for the purpose of regulatingthe tension in the intercostal spacesand of rotating the thorax in its longaxis. By observations on living animalsin which all the muscles of respirationwere excluded except the intercostals,it has now been made clear that the outer layer, as well as that part of the inner included between the costal carti-lages, serves to elevate the ribs, while the remainder of the inner layer drawsthe ribs down (Bergendal and Bergman, E,. Du Bois-Reymond and ^lasoin, ). In the rabbit at least the intercostal muscles are the most important so faras the thoracic breathing is concerned. When greater demand is made upon themuscles of inspiration, the levatores costanim and the scaleni are added levatores alone are able to look after the respiratory movements for a cer-tain time, and their action in the cat is very important (Koraen and B. Moller).Since these muscles are inserted quite close down to the hinder ends of the Fig. 124. The thorax seen from the rightide, after Spalteholtz. 316 RESPIRATION they can, with very slight contraction, produce verj- marked movements of theanterior ends. In the rabbit with more vigorous respiration the serrati postici superiores,the sternohyoidei and the sternothyroidei come into play. In man, finally,Duchenne has found that in the greatest respiratory distress the following mus-cles are active: the sternocleido mastoids which lift the sternum when the head isfixed; the pectorales minores which lift the third to the fifth ribs with the scapulafixed; the serrati aiitici magrii, the pectorales majores and the suhclavii. C. MOVEMENTS OF THE DIAPHRAGM The diaphragm springs from the entire inner surface of the lower edge ofthe thoracic skeleton; its fibers converge toward the axis of the body, and attachthemselves to the flat tendon situated in the center of the muscle. It presents
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectphysiology, bookyear1
