PHYSIOLOGICAL ANATOMY OF THE RESPIRATORY ORGANS 91 



tached to the arytenoid cartilages, are capable of separating and approxi- 

 mating the points to which the vocal chords are attached posteriorly, so 

 as to open and close the rima glottidis. 



In man, the respiratory movements of the glottis have been studied 

 by means of the laryngoscope. In tranquil respiration, the rima glottidis 

 is opened to a certain extent in inspiration, by the tonic contraction of 

 the posterior crico-arytenoid muscles, and its form is triangular ; it is a 

 little narrower in expiration ; but in forced, rapid or difficult breathing, 

 the crico-arytenoids act vigorously and the glottis is widely opened with 

 each inspiration, the opening being somewhat elliptical. In the cadaver, 

 the width of the opening of the glottis is reduced about one-half. The 

 muscles concerned in the respiratory movements of the glottis are ani- 

 mated by the recurrent laryngeal nerves, but the filaments going to these 

 muscles are not derived from the spinal accessory. While the recurrents 

 also contain filaments, derived from the accessories, that preside over the 

 vocal movements of the glottis, these movements are quite distinct from 

 those connected with the act of inspiration. The true vocal sounds are 

 expiratory. 



Attached to the anterior portion of the larynx, is the epiglottis, a leaf- 

 shaped lamella of elastic cartilage, which, during ordinary respiration, pro- 

 jects upward and lies against the base of the tongue. During deglutition, 

 respiration is momentarily interrupted, and the air-passages are protected 

 by the muscles that approximate the vocal chords and by the tongue, 

 which presses backward, carrying the epiglottis before it and completely 

 closing the glottis. Physiologists have questioned whether the epiglottis 

 be necessary to the complete protection of the air-passages ; and it has fre- 

 quently been removed from the lower animals, apparently without inter- 

 fering with the deglutition of solids or liquids. 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, observed in 

 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 show that the presence of the 

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

 tection of the air-passages in deglutition. 



Passing down the neck from the larynx toward the lungs, is the tra- 

 chea, which is four to four and a half inches (10.16 to 11.43 centimeters) 

 in length and about three-quarters of an inch ( 19. 1 millimeters) in diameter. 

 It is provided with cartilaginous rings, sixteen to twenty in number, 

 which partly surround the tube, leaving one-third of its posterior portion 

 occupied by fibrous tissue mixed with non-striated muscular fibres. Pass- 

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



