ANATOMY. 
Jium is a larger space in front of the bodies 
of the vertebrae ; it contains the descend- 
ing aorta, tire vena azygos, thoracic duct, 
'esophagus, and the par vagum. 
The capacity of the chest taken altoge- 
ther varies according as we estimate it in a 
state of inspiration or expiration; being 
largest in the former, and smallest in the lat- 
ter state. The right bag of the pleura is 
considerably larger than the left, as is also 
the right lung. 
Tn the living state the lung is in close con- 
tact with the surface of the cavity, and fol- 
lows all the motions of the sides of the chest. 
It is distended by the influx of air, when the 
chest is enlarged ; and the air is expelled 
from the lung, when the chest is diminished. 
As soon as the thorax is opened in the dead 
subject, the lung falls down from the sides 
of the chest, or in technical language col- 
lapses ; and then a large empty space is seen 
between it and the ribs. From this repre- 
sentation it should appear, that the lungs are 
quite passive in the business of respiration. 
The lungs are two in number ; one being 
contained in each bag of the pleura. They 
are loose and unconnected in these bags, 
except at one point, towards the upper and 
posterior portion of each viscus, where the 
great vessels enter them, and where the bag 
of the pleura is continuous with the reflect- 
ed portion of the membrane. These are 
called the ligaments of the lungs. 
Their colour varies considerably. It is 
always verging more to a red in proportion 
as the subject is younger ; in the adult it has 
more of a spotted and livid cast. Towards 
the back of the lungs it is always much 
deeper from the gravitation of blood in the 
vessels in consequence of the position of the 
subject. It is lighter when the lungs con- 
tain much ah-. 
The lungs are subdivided into lobes ; of 
which the light contains three, and the left 
two. Their substance is composed of a con- 
geries of minute membranous cells, about 
equal in size to a pin’s head, and as these 
are more or less filled with air, they give 
the lung a peculiar spongy feel. These ceils 
communicate with the ultimate ramifica- 
tions of the air vessels, and receive air from 
that source. The pulmonary vessels ramify 
minutely in them, and thereby expose the 
blood to the effects of the contained air ; 
and in tins exposure the object of respira- 
tion is effected. 
The windpipe. The tube, which conveys 
the external air into the lungs, may be di- 
vided into three parts; the larynx, the tra- 
chea, and the bronchi. 
The larynx is a hollow cartilaginous or- 
gan, placed at the top of the trachea. The 
air which passes through this from the lungs, 
in expiration, produces the voice. 
The cavity of the larynx opens above at 
the root of the tongue, and below into the 
trachea. The organ is composed of five 
pieces of cartilage : viz. the thyroid and cri- 
coid cartilages, and epiglottis, and two ary- 
tenoid cartilages. 
The thyroid cartilage is the largest, and 
consists of two irregularly quadrangular- 
pieces, united in front at an obtuse angle. 
Tin's part projects in the front of the neck, 
and much more conspicuously in the male 
than in the female sex : it is called pomum 
Adami. 
The cricoid cartilage may be compared 
to a ring with a seal, of which the broad or 
seal part is placed behind, and the narrower 
portion in front. It is directly under the 
thyroid cartilage. 
The arytenoid are two pyramidal por- 
tions of cartilage, connected by regular 
moveable articulations to the back of the 
cricoid. 
The epiglottis is the softest cartilage of 
the larynx. It has a basis firmly tied to the 
thyroid cartilage ; while its opposite extre- 
mity, which is very thin, is of a rounded fi- 
gure, and stands directly upwards, except 
during deglutition, when it descends so as 
to cover the opening of the larynx. 
The thyroid cartilage is tied by three li- 
gaments to the os hyoides above, and by as 
many to the cricoid cartilage below : but 
the most important ligaments of these parts 
are the ligamenta glotcidis; which arise 
from the front of the arytenoid cartilages, 
and are attached to the posterior surface of 
the front portion of the thyroid. A longi- 
tudinal slit, called the rima glottidis, is left 
between these, and it is by the passage of 
the air through that slit that the voice is 
formed. Hence, from the great share 
which these ligaments have in forming the 
voice, the name of chorda; vocales has been 
given to them. 
The larynx is lined by a vascular and 
very sensible membrane, copiously moisten- 
ed with mucus, in order to defend it from 
the external air. It admits of free motion 
in the neck, and its par ts are also moved 
on each other ; particularly the arytenoid 
cartilages, whose movements, by altering 
the size of the ruina glottidis, and the state 
of tension of the chord® vocales, contr-ibu e 
most immediately to the variations in the 
tone of the voice. 
The trachea is that portion of the aerial 
