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Credit: Respiration / by John Reid. Source: Wellcome Collection.
Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.
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![especially in the female, by the scaleni muscles. W hen the respiration becomes hurried or more laboured, the diaphragm and the muscles that elevate the ribs not only act more vigorously in inspiration, but numerous other muscles, which may be termed auxiliary muscles of inspiration, act in unison with these.* * In cases of great dyspnoea, as in a fit of asthma, the shoulders are fixed, the head is thrown back, and all the auxiliary muscles of inspi- ration are brought into violent action. When the shoulders are fixed by the action of the levatores anguli scapulae, the rhombodei ma- jores et minores, and the humeri also fixed by the scapulo-humeral muscles, or by the person grasping some fixed object by the hands, then the muscles, or portions of them which pass between the thoracic extremities and the an- terior and lateral walls of the chest, as the serrati magni, the pectorales minores et ma- jores, the subclavi, and perhaps the costal portion of the latissimi dorsi, act as muscles of inspiration, by pulling the ribs upwards and outwards j ; and when the head, cervical vertebras, hyoid bone, and larynx are fixed by the numerous muscles capable of performing this action, then the sterno-cleido-mastoidei, the sterno-hyoid, and sterno-thyroid muscles, may aid the scaleni muscles in drawing the superior part of the thorax upwards.^ The serrati postici superiores, and the cervicales descendentes, are also accessory muscles of inspiration, if the former be not, at times, in fact a muscle of ordinary inspiration. The su- perior aperture of the larynx is dilated during inspiration by the crico-arytenoidei postici muscles when the breathing is in the least that both sets are muscles of expiration, while the latter maintains the more probable opinion, that they act differently in different parts of the thorax. Dr. Hutchinson has also lately made some obser- vations on the actions of these muscles in Medico- Chirurgical Transact, of London, vol. xxix. p. 213. [Dr. Hutchinson regards the external intercostals and the intercostilaginous portion of the internal in- tercostals as muscles of inspiration, while the rest of the internal intercostals are muscles of expiration. See a further exposition of this author’s views in the article Thorax.—Ed.] * According to Dr. Hutchinson (Opus cit. p. 187) the chief enlargement of the thoracic cavity in deep inspiration is made by the ribs, and not by the diaphragm. f .Part of the muscles passing between the thoracic extremities and the anterior and lateral walls of the chest, here enumerated among the accessory muscles of inspiration, may, in certain cases, act as accessoiy muscles of expiration, by drawing the scapula; for- cibly downwards upon the ribs. (Vide observa- tions of Mr. Sibson and MM. Beau and Maissiat.) These authors are not of the same opinion regarding the action of all these muscles; for, while the two former class the serratus magnus among the muscles of inspiration (Opus cit. tom. iii. p. 2G8. 1843), the latter affirms that the greater portion of its fasciculi acts visibly in violent expiration (Opus cit. p. 535) ; they agree, however, in placing the latissimus dorsi among the accessory muscles of expiration. J The hyoid bone, larynx, and trachea are some- times drawn downwards during violent inspirations by the strong contractions of the sterno-hyoid and sterno-thyroid muscles, causing a depression of these parts, at the same time that they elevate the sternum. hurried; and in laboured breathing the nos- trils are expanded by the contraction of the muscles, which draw the alae of the nostrils outward. The greater or less demand for fresh air in the lungs regulates the number of these accessory respiratory muscles brought into play, and the energy of their contraction. A diminution of the capacity of the thorax or an act of expiration, by which part of the air is expelled from the lungs, follows imme- diately each inspiratory movement. In ordi- nary respiration, after the muscles of inspi- ration have ceased to contract, the elasticity of the thoracic walls, especially of the carti- laginous portion, causes it to return to the state in which it was before its dilatation ; and when the contracted diaphragm has re- laxed, the elasticity of the parts displaced by its descent, is sufficient, without much, if any, aid from the abdominal muscles, to push the diaphragm again upwards. The gas present in greater or less quantity in the digestive tube, being compressed during the descent of the diaphragm, will, from its elasticity, assist in pushing upwards the relaxed diaphragm.* In more forcible expirations, when the walls of the chest are compressed beyond the state they assume when the muscles of inspiration are relaxed, the compressing muscles expe- rience considerable resistance from the elas- ticity of the walls of the chest. When the expirations are performed more forcibly than ordinarily, the diaphragm is pushed up, and the sternum and ribs de- pressed by the contractions of the three broad muscles of the abdomen, by the recti abdo- minis, and by the triangularis sterni muscles. The levator ani, one of the antagonist muscles of the diaphragm, assists also in pushing the abdominal viscera upwards. In hurried or laboured expirations the diaphragm is pushed more forcibly upwards by the muscles mentioned, and the ribs are pulled downwards, and the chest compressed, by the quadrati lumborum, serrati postici inferiores j-, sacro-lumbales and longissimi dorsi muscles. MM. Beau and Maissiat J have described three kinds of ordinary respiratory move- ments : 1. the abdominal, in which the abdo- minal walls chiefly act: 2. the costo-inferior, in which the movements chiefly take place in the lower ribs, from the seventh inclusive, downwards: 3. the costo-superior, in which the superior part of the chest is carried up- wards by the elevation of the superior ribs ami the sternum. The first kind, or the ab- dominal type, is observed in infants up to the end of the third year in both sexes ; but after this period the costo-superior type in girls, and the costo-inferior and abdominal types in boys, generally prevail, and this difference becomes more marked as they advance in years. Almost all men, therefore, breathe by * Maissiat, in liis Etudes do Physique Aniinale, and Beau and Maissiat in Arch. Gener. do Med. tom. iii. p. 263. 1843. t Dr. Hutchinson informs us that the body is considerably shortened during violent expiration. (Op. cit. pp. 191, 192.) J Archiv. Gen. de Med. tom. xv. p. 399. 1842. n 2](https://iiif.wellcomecollection.org/image/b2238618x_0013.jp2/full/800%2C/0/default.jpg)
