The lymphatic system in most animals, but 
particularly in man and quadrupeds, is full of 
valves. These valves have been painted by 
the celebrated Nuek, Ruysch, and others, 
and are much more frequent than in the com- 
mon veins; and thence these lymphatics have 
sometimes been distinguished by the name of 
valvular lymphatic vessels. Those valves are 
generally two in number, are of a semilunar 
shape, and one is sometimes much larger 
than the other. In some parts of the body, 
these valves are so numerous, that there are 
three or four pair in an inch of space ; but 
sometimes there is no more than one pair, 
sometimes several inches of a lymphatic ap- 
pear without a valve. They are less nume- 
rous in the thoracic duct than in the branches 
of the system. Thence it might be supposed, 
that in proportion as we go from the trunk to 
the branches, we should find them thicker 
set. But' this not always true; for Mr. Idew- 
son observed them more numerous in the 
lymphatic vessels of the thigh than on those 
of the leg. When the vessels are distended 
with lymph, they appear larger on that side 
of the valves next the heart, which sometimes 
gives a lymphatic vessel an appearance of 
being made of a chain of vesicles ; as sfich they 
are represented by some authors ; but it is an 
appearance that very seldom occurs in the 
human body. In quadrupeds, however, this 
appearance is very remarkable. Wherever a 
lymphatic vessel enters the thoracic duct, we 
i ind either one or two valves which prevent 
the return of the lymph. 
Lastly, the lymphatic system in different 
parts of its course has the glands, called con- 
globate or lymphatic. These glands are so 
placed, that the vessels come in on one side, 
and pass out on the other, in thdr way to the 
thoracic duct. They are commonly of an 
oval, though sometimes of a round shape, and 
frequently somewhat flattened, and of various 
sizes; some being no larger than a millet seed, 
while others are almost an inch in diameter. 
They vary in colour in different parts of the 
body, and at different times of life. In young 
people they are generally of a reddish or 
brown colour, but become paler with age. 
They have a shining external surface, which 
is owing to a smooth dense coat that covers 
them. Like other glands, they have arteries, 
veins, and nerves, which enter into their com- 
position ; but with respect to the rest of their 
structure, anatomists are much divided in 
opnion. Soemmerring has endeavoured to 
prove that they are partly cellular and partly 
vascular. That these glands are wanting in 
some animals is now known. 
The absorbent system, besides the glands, 
is divided into three parts, viz. the lacteal, 
the lymphatic vessels and the lacteal sac, and 
the lymphatic duct. The lacteals belong to 
the intestinal tube, the lymphatics to all the 
other parts of the body, and the lacteal sac 
and thoracic duct is the common trunk which 
receives both the lacteals and lymphatics. 
We shall give a particular description of the 
latter from the celebrated Monro, as being 
that part of the absorbent system which is 
most important, both to the general reader 
and to the medical student. 
“ The receptaculum chyli, or saccus lac- 
feus, is a membranous, somewhat pyriform 
bag, two-thirds of an inch long, one-third of 
,an inch over in its largest part when collapsed ; 
situated on the first vertebra of the loins of the 
ANATOMY. 
right of the aorta, a little higher than the 
right emulgent artery, behind the right infe- 
rior muscle of the diaphragm ; it is formed by 
the union of three tubes, one from under the 
'aorta, the second from the interstice of tjie aor- 
ta and cava, the third from under the emul- 
gents of the right side. 
“ The lacteal sac becoming gradually 
smaller toward its upper part, is contracted 
into a slender membranous pipe, of about a 
line diameter, which is generally .named the 
thoracic duct. This passes betwixt the mus- 
cular appendices, or inferior muscles of the 
diaphragm, on the right of, and somewhat be- 
hind the aorta; then being lodged in the cellular 
substance, behind the pleura, it mounts be- 
tween the aorta and the vena azygos, as far as 
the fifth vertebra of the thorax, where it is hid 
by the azygos, as this vein rises forward to 
join the descending or superior cava; after 
which the duct passes obliquely over to the 
left side behind the oesophagus, aorta de.-cen- 
. dens, and the great curvature of the aorta, 
until it reaches the left carotid artery ; behind 
which, on the Ifc-ft side of the oesophagus, it 
runs to the interstice of the first and second 
vertebra; of the thorax, where it begins to se- 
parate from the carotid, stretching further to- 
ward the left internal jugular vein by a cir- 
cular turn, whose convex part is uppermost. 
At the top cf this arch it splits into two for a 
line and a half; the superior branch receiving 
into it a large lymphatic vessel from the cer- 
vical glands. This lymphatic appears by 
blowing air and injecting liquors into it, to 
have few valves. When the two branches are 
again united, the duct continues its course to- 
ward the internal jugular vein, behind which 
it descends, and immediately at the left side of 
the insertion of this vein, enters the superior 
posterior part of the left subclavian vein, whose 
internal membrane duplicated forms a semi- 
lunar valve, that is convex externally, and 
covers two-thirds of the orifice of the duct; 
immediately below this orifice, a cervical vein 
from the musculi scaieni enters the subcla- 
vian. 
“ The coats of the sac and duct are thin 
transparent .membranes, from the inside of 
which, in the duct, small semilunar valves are 
produced most commonly in pairs, which are 
so situated, as to allow the passage of liquor 
upward, but oppose its return in an opposite 
course. The number of these is generally ten 
or twelve. _ 
“ This is the most simple and common 
course, situation, and structure, of the recep- 
taculum chyli, and thoracic duct.” 
Of the heart, lungs, and arterial system. 
Previous to describing the arterial system 
of the human body, it will be necessary to 
give a general account of the thorax and its 
contents. 
By the thorax we commonly understand all 
that part of the body which answers to the ex- 
tent of the sternum, ribs, and vertebras of the 
back, both outwardly and inwardly. 
The thorax is divided into the anterior 
part, called commonly the breast; the poste- 
rior part called the back, and the lateral parts 
called the right and left sides. 
The internal parts cf the thorax are con- 
tained in the cavity or the portion of the trunk, 
which is. named the cavity of the breast. 'Phis 
cavity is lined by a membrane called pleura, 
which forms the mediastinum, and contains 
the heart and lungs, with the vessels, & c . 
which go into or out from them ; through it 
likewise the oesophagus passes to the stomach, 
and part of the nerves are contained in it 
which go to the contents of the abdomen. 
, Carit U °J ^ ie thorax. The hard parts 
which form the sides of this cavity, are. the 
twelve vertebra? of the back, all the ribs, and 
the sternum. 'I he soft parts, which complete 
the sides, are, the membrane called pleura, 
which lines the cavity, and the musculi inter- 
costales, sterno-costales* and diaphragma, al- 
ready described. ° 
All these hard and soft parts taken together 
represent a kind of cage, in some measure of 
a conical figure, flatted on the foreside, de- 
pressed on the back side, and in a manner di- 
vided into two nooks, by the figure of the ver- 
tebra of the back, and terminated below a 
broad arched basis, inclined backward. The 
intercostal muscles fill up the intestines be- 
twixt the ribs, and so complete the sides of 
the cavity. r i he basis is the diaphragm ; and 
the pleura not only covers the whole inner 
surface of the cavity, but by forming the me- 
diastinum, divides *it into two, one on tiie 
right, the other on the left. 
Pleura and mediastinum. 
The pleura is a membrane which adheres 
very closely to the inner surface of the ribs, 
sternum, and musculi intercostales, sub-dos- 
tales, and sterno-costales, and to the convex 
side of the- diaphragm. It is of a very firm 
texture, and is supplied with blood-vessels and 
nerves, in all which it resembles the perito- 
nanun ; and likewise in that it is made up of 
an inner true membranous lamina, and a cel- 
lular substance on the outside. 
Each side of the thorax has its particular 
pleura entirely distinct from the other: and 
making, as it were, two great bladders, situ- 
ated laterally with respect to each other in the 
great cavity of the breast ; in such a manner as 
to form a double septum, or partition, running 
between the vertebra and the sternum, their 
other sides adhering to the ribs and dia- 
phragm. 
This particular duplicature of the two pleu- 
ra* is termed mediastinum: the two lamina; of 
which it is made up are closely united toge- 
ther near the sternum and vertebrae; but in the 
middle, and toward the lower part of the fore 
side, they are separated by the pericardium 
and heart, as we shall see hereafter. A little 
more backward they are parted in a tubular 
form by the oesophagus, to which they serve 
as a covering; and in the most poster, or part 
a triangular space i.s left between the vertebra 
and flie two pleura from above downward, 
wine n is filled chiefly by the aorta. 
i Before the heart, from the pericardium to 
the sternum, the two lamina* adhere very 
closely, and there the mediastinum is transpa- 
rent, except for a small space near the upper 
part, where the thymus gland is situated, so 
that in this place there is -naturally no inter- 
stice, or particular cavity. The apparent se- 
paration is owing entirely to the common 
method of raising the sternum, as was plainly 
demonstrated by Burtholinus in his treatise 
oH iie diaphragm, published at Paris in 1676. 
i he mediastinum does not commonly ter- 
minate along the middle of the inside of the 
sternum, as the common opinion has been. 
Muslow demonstrated, in the year 1715, to 
the Royal Academy of Sciences, that from 
