ANATOMY OF BALiEN OP.TEBA BOSTRATA. 
243 
pressed upwards the contents of the mouth are passed into the pharynx ; the glottis is 
simultaneously closed by the approximation of the arytenoid bodies, which are brought 
together by the arytenoideus proprius and drawn upwards and forwards by the aryteno- 
epiglottidis muscle, when they meet and are overlapped by the tip of the epiglottis, the 
whole being covered by the hood-like fold of mucous membrane, which seems to be 
especially adapted for this purpose. It will be seen that by this admirable contrivance 
all extraneous matter is strictly excluded from the larynx while the food is passing 
through the oesophagus to the stomach. 
The Trachea and Lungs. 
The trachea was continued backwards from the posterior and inferior extremity of the 
larynx for about 5f inches, and terminated opposite the superior aspect of the arch of 
the aorta by bifurcating into the right and left bronchi ; it measured in diameter of 
inches, and its cartilaginous rings, which were irregular, often bifurcating and coalescing, 
formed almost complete circles; the last was peculiar in shape, and consisted of two 
arches united in the centre so as to form the commencement of the two bronchial tubes ; 
this union was much more extensive in front than behind, and the pair of rings im- 
mediately above were joined to it on the anterior aspect by means of a cartilaginous 
plate continued up from the vertex of the angle of union of the lateral halves of the last 
ring. 
The tracheal mucous membrane had a peculiar folded arrangement, being traversed 
by a number of longitudinal sulci, apparently to permit of its being distended. The 
right bronchus bifurcated immediately after its origin, which gave to the termination of 
the trachea the appearance of its being trifurcate : both these bronchi on the right side 
entered the root of the lung at a considerable distance from each other. The upper, or 
what may be termed the accessory division, was much smaller than the inferior, mea- 
suring only 1 inch in diameter, whereas the lower division was nearly 2J inches in the 
same direction. On the left side there was but a single bronchus, whose diameter was 
3 inches. 
The right lung measured 15|- inches in length and 7 inches in width ; the left was 
17 inches long and 6^ inches broad, and passed further forwards than the right. The 
bases of both lungs were much hollowed where they lay in contact with the diaphragm, 
and measured 13 inches in breadth from their anterior to their posterior borders. 
In the root of the right lung the pulmonary artery lay above the bronchus, and the 
two principal pulmonary veins lay below and on a plane anterior to it ; at the top of the 
root a small accessory pulmonary vein passed outwards, lying 3 inches below the trun- 
cated apex of the lung, and 3^ inches above the pulmonary artery. 
On the left side the pulmonary artery lay also above and behind the bronchus, and 
the veins, two in number, were situated one on a level with the bronchus, the other 
about 3 inches more posteriorly. The lining membrane of the pulmonary veins dis- 
played a series of longitudinal plicae similar to those seen in the trachea. The roots of 
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