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- observation to M. Helvef'usT 
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Vascular texture. — All the bronchial cells 
are surrounded by a very fine reticular texture 
of the small extremities of arteries and 
veins, which communicate every way with 
each other. The greatest part of this admi- 
rable structure is the discovery of the illus- 
trious Malphigi. 
Blood-vessels. — The blood-vessels of the 
lungs are of two kinds ; one common, 
called the pulmonary artery and veins; the 
other proper, called the bronchial arteries 
and veins. 
The pulmonary artery goes out from the 
right ventricle of the heart ; and its trunk, 
having run directly upward as high as the 
curvature of the aorta, is divided into two 
lateral branches, one going to the right hand, 
called the right pulmonary artery ; the other 
to the left, termed the left pulmonary artery. 
The right artery passes under the curvature 
of the aorta, and is consequently longer than 
the left. They both run to the lungs, and 
are dispersed through their whole substance 
by ramifications nearly like those of the 
bronchia, and lying in the same direction. 
The pulmonary veins having been distri- 
buted through the lungs, in the same manner 
go out on each side by two great branches, 
which open laterally into the reservoir or 
muscular bag of the right auricle. 
'Fhe ramifications of these two kinds of 
vessels in the lungs, are surrounded every 
where by the cellular substance already men- 
tioned, which likewise gives them a tind of 
vagina ; and the rete mirabile of Malphigi, 
described above, is formed by the capillary 
extremities of these vessels. It must be ob- 
served, that the ramifications of the arteries 
are more numerous and larger than those of 
the veins, which in all other parts of the body 
exceed the arteries both in number and 
size. 
Bronchial arteries and veins. — Besides these 
capital blood- vessels, there are others called the 
bronchial arteries and veins, which are very 
small, but they follow the bronchia through 
all their ramifications. They communicate 
with the pulmonary arteries and veins in 
many places, likewise with the arteries and 
veins of the oesophagus, and with branches of 
the coronary artery and vein. These are 
nutrient vessels of the lungs. 
Ligaments. — Under the root of each lung, 
'♦hat is, under that part formed by the subor- 
dinate trunk of the pulmonary artery, by the 
trunks of the pulmonary veins, and by the 
trunk of the bronchia, there is a pretty broad 
ligament, which ties the posterior edge of 
-each lung to the lateral parts of the vertebrae 
of the back from the root all the way to the 
, diaphragm. 
Trachea arteria. — The bronchia, already 
described, are branches or ramifications of a 
large canal, partly cartilaginous, and partly 
membranous, called trachea, or aspera arte- 
ria. It is situated anteriorly in the lower 
part of the neck, whence it runs down into 
the thorax between the two pleurae through 
the upper space left between the dnplicature 
of the mediastinum, behind the thymus. 
Having reached as low as the curvature of 
the aorta, it divides into lateral parts, one to- 
ward the right hand, the other toward the 
left, which enter the lungs, and are distribut- 
ed through them in the manner already said. 
ANATOMt. 
These two branches are called bronchia ; and 
U,<M - — right side is shorter than that of 
the left, whereas the right pulmonary artery 
is the longest. 
The trachea is made up of segments of 
circles of cartilaginous hoops, disposed in 
such a manner as to form a canal, open on 
the buck part of the cartilages, not going quite 
round ; but this opening is filled by a soft 
glandular membrane, which completes the 
circumference of the canal ; but this cannot 
be to give way to the oesophagus : for, instead 
of descending immediately upon the middle 
of that canal, the trachea inclines a little to 
the right side ; and the same structure is 
formed in the back part of the bronchial ves- 
sels, which are at some distance from the 
oesophagus. 
Each circle is about the twelfth part of an 
inch in breadth, and about a quarter of that 
space in thickness. Their extremities aTe 
round ; and they are situated horizontally 
above each other, small interstices being left 
between them, and the lower edge of the su- 
perior segments being turned toward the up- 
per edge of those next below them. 
They are all connected by a very strong 
elastic membranous ligament iixed to their 
edges. 
The trachea is covered externally with a 
quantity of cellular substance, which unites 
it to the neighbouring parts, and it is lined on 
the inside by a particular membrane ; which 
appears to be partly fleshy or muscular, and 
partly ligamentary, perforated by an infinite 
number of small holes, more or less imper- 
ceptible, through which a mucilaginous fluid 
cbntinually passes, to defend the inner sur- 
face of the trachea against the acrimony of 
the air which we breathe. 
This iluid comes from small glandular bo- 
dies dispersed through the substance of the 
membrane, but especially from glands some- 
thing larger than the former, which lie on 
tire outer or posterior surface of that strong 
membrane by which the circumference of 
the canal is completed. The same structure 
is observable in the ramifications of the tra- 
chea, from the greatest to the smallest. 
All the vessels of which the lungs are 
chiefly composed, that is, the air-vessels or 
bronchia, and the blood-vessels or the pul- 
monary and bronchial arteries and veins, ac- 
company each other through this viscus. 
They are disposed commonly in such a 
manner, even to the last ramifications, as 
that a subordinate trunk or branch of the 
bronchia lies between lire like trunks or 
branches of the pulmonary artery and vein ; 
the bronchial vessels being immediately join- 
ed to the bronchia. In some places these 
three kinds of vessels touch each other in 
such a manner as to have a triangular space 
in the middle. 
The bronchia are divided into a very great 
number of ramifications ; and the last raini 
are the pedicles or footstalks of the small lo- 
buli. All the lobuli are angular, oblong, 
broad, thin, &c. The footstalks send out 
other smaller membranous pedicles, which 
are very short, and terminate in the bron- 
chial vesicles or cells, of which they are 
continuations. The subordinate trunks and 
rami detach a great number of these pedicles 
from their convex surface. 
When we blow into the lungs, the bronchial 
cells nearest their outer surface appear like 
small portions of round vesicles ; and frona 
this appearance all the bronchial cells have 
got the name of vesicles, though they are all 
angular, except those which we have now 
mentioned. 
When we examine a lung without blowing 
it up, we find that the cartilaginous segments 
of the bronchia lie so near as to be engaged 
in each other ; and in drawing out any por- 
tion of the bronchia by two ends, these seg- 
ments are parted, and the whole canal is in- 
creased in length ; but it contracts again, by 
means of its elastic membrane, as soon as 
that force is taken off. 
When we open lengthwise any portion, 
of the pulmonary artery and vein in the same 
lung, we meet with a great number of trans- 
verse rugae, which are destroyed when these 
vessels are elongated. This is an observa- 
tion made by M. Helvetius. 
By virtue of this structure all the ramifica- 
tions, both of the bronchia and pulmonary 
arteries and veins, have constantly the same 
direction whether the lung be inflated or col- 
lapsed : and they contract in length without 
being contorted or folded. In expiration 
these vessels are elongated, and shortened in 
inspiration. 
These three vessels lie in a sort of cel- 
lular vagina, which accompanies all their ra- 
mifications, and is a continuation of their in- 
terlobular cells. The pellicula; which com- 
pose it are, however, there disposed in a more 
regular manner, and more longitudinally than 
in other places, and thereby appear to form 
a true vagina. 
When we blow through a pipe, introduced 
so far as to touch immediately a trunk of the 
blood-vessels or bronchia, the air runs through 
all the cells that lie nearest that trunk or its 
branches ; but if we continue to blow, it in- 
sinuates itself through the whole interlobular 
substance. 
Bronchial glands. At the angle of the first 
ramification of the trachea arteria, we find 
on both the fore and the back sides cer- 
tain soft, roundish, glandular bodies, of a 
bluish or blackish colour, but reddish in a 
child ; in size they vary from that of a field 
bean to that of a millet-seed. Through these 
the lymphatic vessels of the lungs pass in 
their way to the thoracic duct. 
The trachea has several coats, as has been 
already observed. The outermost or common 
covering surrounds that part of the trachea 
which lies in the thorax ; but out of the thorax 
this first coat is derived from the aponeurotic 
expansions of the muscles of the neck ; 
and it is between this and the following co- 
vering that the glands, already mentioned, are 
situated. 
The second is a proper coat, being a con- 
tinuation of the cellular covering of the lungs ; 
the pellicula; of which, near the cartilaginous 
segments, serve them for an external pericar- 
dium. The third membrane lies on the in- 
side, adhering closely to the same cartilages, 
and supplying to these the place of an internal 
pericardium. 
The fourth membrane is that which com- 
pletes the circumference of the cartilaginous- 
circles of the trachea. It consists chiefly of 
two laminae or strata, partly muscular and 
partly tendinous : the external or posterior 
lamina being made up of longitudinal fibres ; 
and the internal or anterior of transverse fibres. 
The membrane is perforated by tire small 
