fab RESPIRATORY sysTEM.: 
THE ORGANS OF RESPIRATION AND VOICE. 
sy D. J. CUNNINGHAM. 
THE organs of respiration are the larynx and trachea, which together constitute a 
wide median air-passage ; the two bronchi or branches into which the lower end of 
the trachea divides; and the two lungs to which the bronchi conduct the air. In 
connexion with the lungs we have likewise to consider 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 these organs. 
The larynx opens above into the lower part of the pharynx, and the air which 
passes in and out from the air-passages likewise traverses the pharynx, the nasal 
fossze, and also the buccal cavity if the mouth is 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 front aspect of the 
primitive fore-gut of the embryo. In most mammals the upper aperture of the 
larynx opens into the part of the pharynx which hes behind the nasal chambers. 
In man, however, the upper opening of the larynx is placed lower down, below the 
communication between the mouth and pharynx, and both nasal and buccal 
breathing may be carried on with very nearly equal ease. 
THE LARYNX OR ORGAN OF VOICE. 
The larynx is the upper part of the air-passage, specially modified for the pro- 
duction of the 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 in front of the bodies of the fourth, 
fifth, and sixth cervical vertebre. Its highest point, represented by the tip of the 
epiglottis, reaches as high as the lower border of the body of the third cervical 
vertebra, whilst its lower limit usually corresponds to the lower border of the body 
of the sixth cervical vertebra. From the vertebral column the larynx is separated, 
not only by the prevertebral muscles and prevertebral layer of cervical fascia, but 
also by the posterior wall of the pharynx—indeed, the posterior surface of the 
larynx forms the lower part of the anterior wall of the pharynx, and is covered by 
the lining mucous membrane of that section of the alimentary canal. 
The larynx les 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 front of the neck, and in the median line it approaches very close to the sur- 
face, being merely covered by skin and the two layers of fascia. Laterally it is 
more deeply placed. Thus it is overlapped by the sterno-mastoid muscle, covered 
by the two strata of thin ribbon-like muscles which are attached to the thyroid 
cartilage and the hyoid bone, and hidden to some extent by the upward prolonga- 
tions of the lateral lobes of the thyroid body. 
The position of the larynx is influenced by movements of the head and neck. ‘Thus it 
is elevated when the head is thrown back, and depressed when the chin is carried down- 
