THE RESPIRATORY SYSTEM. 



THE ORGANS OF RESPIRATION AND VOICE. 



By the late D. J. CUNNINGHAM, F.R.S., 



Professor of Anatomy, University of Edinburgh. 



Kevised by KICHARD J. A. BERRY, F.E.C.S., 



Professor of Anatomy, University of Melbourne. 



THE organs of respiration are the larynx and trachea, which, together, constitute a 

 median air-passage ; the two bronchi or branches into which the inferior end of the 

 trachea divides; and the two lungs to which the bronchi conduct the air. In 

 connexion with the lungs there are also the pleural membranes two serous sacs 

 which line the portions of the thoracic cavity which contain the lungs, and at 

 the same time give a thin coating to those organs. 



The larynx opens above into the inferior or caudal part of the pharynx, and 

 the air which passes in and out from the air -passages likewise traverses the 

 pharynx, the nasal cavity, and also the oral cavity if the mouth be open. This 

 connexion between the digestive and respiratory systems is explained by the 

 fact that the respiratory apparatus is secondarily developed, as an outgrowth, 

 from the ventral aspect of the primitive fore -gut of the embryo. In most 

 mammals the superior or cranial aperture of the larynx opens into the part of 

 the pharynx which lies immediately dorsal, or posterior, to the nasal cavities. 

 In man, however, the superior opening of the larynx is placed below, that is 

 inferior or caudal to, the communication between the mouth and pharynx, and 

 both nasal and oral breathing may be carried on with very nearly equal ease. 



The 



LARYNX. 



ie larynx or organ of voice is the upper part of the air-passage, specially 

 modified for the production of voice. Above it opens into the pharynx, whilst 

 below its cavity becomes continuous with the lumen of the trachea or windpipe. 



Position and Relations of the Larynx. In the natural position of the neck, 

 and whilst the organ is at rest, the larynx is placed on the ventral side of the 

 bodies of the fourth, fifth, and sixth cervical vertebrae. Its highest point, 

 represented by the tip of the epiglottis, extends to the inferior border of 

 the body of the third cervical vertebra, whilst its lowest limit (the inferior 

 border of the cricoid cartilage) usually corresponds to the inferior border of the 

 body of the sixth cervical vertebra. From the vertebral column the larynx is 

 separated, not only by the prevertebral muscles and the prevertebral fascia, but 

 also by the dorsal wall of the pharynx indeed the dorsal surface of the larynx 

 forms the inferior part of the ventral or anterior wall of the pharynx, and is 

 covered by the lining mucous membrane of that section of the alimentary canal. 



The larynx lies below the hyoid bone' and the tongue, and in the interval 

 between the great vessels of the neck. It forms a more or less marked projection 

 on the ventral side of the neck, and, in the median plane, it approaches very closely 

 to the surface, being merely covered by skin and the two layers of fascia. Laterally 



1061 



