Archive image from page 338 of The cyclopædia of anatomy and. The cyclopædia of anatomy and physiology cyclopdiaofana05todd Year: 1859 RESPIRATION, ORGANS OF. is not the result of atmospheric pressure, nor of the action of the thoracic inspiratory mus- cles : it is due to the elastic property of the cartilaginous pieces. A ' membranous inter- val ' in the walls of the mtra-pulmonary bronchi would obviously expose the air-pas- sages to injurious pressure. The muscular fibres which always belong to the unstriped kind in this class of bronchial tube are ar- ranged chiefly circularly, but partly
Archive image from page 338 of The cyclopædia of anatomy and. The cyclopædia of anatomy and physiology cyclopdiaofana05todd Year: 1859 RESPIRATION, ORGANS OF. is not the result of atmospheric pressure, nor of the action of the thoracic inspiratory mus- cles : it is due to the elastic property of the cartilaginous pieces. A ' membranous inter- val ' in the walls of the mtra-pulmonary bronchi would obviously expose the air-pas- sages to injurious pressure. The muscular fibres which always belong to the unstriped kind in this class of bronchial tube are ar- ranged chiefly circularly, but partly longi- tudinally. They are thus enabled, not only to contract the calibre, but to diminish the length, acting, therefore, as important expiratory powers. As the dissector advances towards the branches of the ' bronchial tree,' the cartila- ginous fragments in the walls of the tubes be- come thinner and smaller, and more and more distantly placed, until eventually they cease altogether, the walls of the tubes being com- posed of nothing but fibro-membrane. Here the tubes are maintained in the open state in part by the expansive force of the contained column of air. The collapse of these pas- sages leads to the atalectasis of that portion of the lung to which they lead. At this point the gravest impediment to respiration, in bronchitis, occurs; here also is chiefly seated the obstacle to expiration in some forms of emphysema; and these musculo- membranous tubules are the scene of spasm during the paroxysms of spasmodic asthma. The parietes of the bronchial tubes Fig. 208. A section of a minutely injected piece of human lung. (After Rainey.) The section cuts longitudinally a branching bronchial tube. At a, the ciliated epithelium of this tube is seen to terminate by an abruptly de- nned border, illustrating the doctrine held by Mr. Rainey, which contends for the complete absence of all epithelium from all parts of the lung beyond this limit, b marks the sudden manner in whic
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