ANATOMY OF THE RESPIRATORY ORGANS. Ill 



the thyroid cartilages, and posteriorly, to the movable arytenoid cartilages. 

 Air is admitted to the trachea through an opening between the chords, which 

 is called the rima glottidis. Little muscles, arising from the thyroid and cri- 

 coid and attached to the arytenoid cartilages, are capable of separating and 

 approximating the points to which the vocal chords are attached posteriorly, 

 so as to open and close the rima glottidis. 



If the glottis be exposed in a living animal, certain regular movements are 

 presented, which are synchronous with the acts of respiration. The larynx 

 is slightly opened at each inspiration, by the action of the muscles referred to 

 above, so that the air has a free entrance to the trachea. At the termination 

 of the inspiratory act these muscles are relaxed, the vocal chords fall together 

 by their own elasticity, and in expiration, the chink of the glottis returns to 

 the condition of a narrow slit. The expulsion of air from the lungs in tran- 

 quil respiration is a passive process and tends in itself to separate the vocal 

 chords ; but inspiration, which is active, were it not for the movements of 

 the glottis, would have a tendency to draw the vocal chords together. The 

 muscles which are concerned in producing these movements are animated by 

 the inferior laryngeal branches of the pneumogastric nerves. The respiratory 

 movements of the larynx are entirely distinct from those concerned in the 

 production of the voice. 



Attached to the anterior portion of the larynx, is the epiglottis, a little, 

 leaf -shaped lamella of fibre-cartilage, which, during ordinary respiration, pro- 

 jects upward and lies against the posterior portion of the tongue. During 

 the act of deglutition, respiration is momentarily interrupted, and the air- 

 passages are protected by the tongue, which presses backward, carrying the 

 epiglottis before it and completely closing the opening of the larynx. Physi- 

 ologists have questioned whether the epiglottis be necessary to the complete 

 protection of the air-passages ; and it has frequently been removed from the 

 lower animals without apparently interfering with the proper deglutition of 

 solids or liquids (Magendie). It is a question, however, whether the results 

 of this experiment can be absolutely applied to the human subject. In a case 

 of loss of the entire epiglottis, which was observed in the Bellevue Hospital, 

 the patient experienced slight difficulty in swallowing, from the passage of 

 little particles into the larynx, which produced cough. This case, and others 

 of a similar character which are on record, show that the presence of the 

 epiglottis, in the human subject at least, is necessary to the complete protec- 

 tion of the air-passages in deglutition. 



Passing down the neck from the larynx toward the lungs, is the trachea, 

 which is four to four and a half inches (10'16 to 11 '43 centimetres) in length 

 and about three-quarters of an inch (19'1 mm.) in diameter. It is provided 

 with cartilaginous rings, sixteen to twenty in number, which partially sur- 

 round the tube, leaving about one-third of its posterior portion occupied by 

 fibrous tissue mixed with a certain number of non-striated muscular fibres. 

 Passing into the chest, the trachea divides into the two primitive bronchia, 

 the right being shorter, larger and more horizontal than the left. These 

 tubes, provided, like the trachea, with imperfect cartilaginous rings, enter the 



