Clinical tuberculosis . act is lessened, and they are also dejirived of the fullcompressing force of the contracting diaphragm upon the ab-dominal viscera. Wenckebach has aptly compared the compres- MECHANICS OF RESPIUATION 327 sing action of tlie contracting diaphragm upon the liver to thaiof the compression of a hand on a sponge. Anything which interferes with the inspiratory act producesthe ci^cct above described. This may be understood by Fig. 60Aand B. When conditions have arisen in the chest which makeit necessary to call the accessory muscles of respiration into use,any influence interf
Clinical tuberculosis . act is lessened, and they are also dejirived of the fullcompressing force of the contracting diaphragm upon the ab-dominal viscera. Wenckebach has aptly compared the compres- MECHANICS OF RESPIUATION 327 sing action of tlie contracting diaphragm upon the liver to thaiof the compression of a hand on a sponge. Anything which interferes with the inspiratory act producesthe ci^cct above described. This may be understood by Fig. 60Aand B. When conditions have arisen in the chest which makeit necessary to call the accessory muscles of respiration into use,any influence interfering with their action will also affect theforce of the inspiratory act. (See page 328.) Muscles Employed in Forced Respiration.—Spasm of tlie acces-sory muscles of respiration becomes an important factf)r in the diag-nosis of tuberculosis because of tlie fact tliat tliey take their nervesujjply from cervical nerves which mediate with intraspinal neuronswhich receive and transmit upward to tliem im])ulses which come. Fig. 59.—Showing the position of the bifurcation of the trachea with the peritrachealand peribronchial glands projected upon the posterior surface of the chest in a youngadult. ( from the inflamed lung, tlie same as just meiititmed for the di-aphragm. This fact will be evident from the following table of accessoi-ymuscles of respiration and their innervation: 1. Scalenus anticus, medius and posticus,—innervated by fila-ments from the cervical and brachial plexuses. 2. Serratus posticus superior, innervated Ity nervus dorsalisscapulfB from the fiftli cervical nerve. 3. Sternocleidomastoideus innervated bv ramus externus 328 PHYSICAL EXAMINATION OF ORGANS OF THORAX nervi aceessorii and lilaments from the second and thii-d cervicalnerves. 4. Trapezius innervated liy ramus externus nervi aceessoriiand tliird and fourth cervical nerves. 5. Rhomboidei innervated by dorsalis scapula- from the fifthcervical nerve. 6. Extensores columna? vertebralis innervat
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