208 
more than five orsix. They maintain their ordi- 
nary size and appearance to within a quarter of 
an inch of the gland, where they suddenly branch 
out, artery-like, into several Rapr RSE Va 4 minute 
vessels which plunge into the gland, thus con- 
veying the lymph,in a minutely divided state 
through this organ to emerge again from it by 
a converse arrangement of equally small vessels, 
which at a quarter of an inch from the gland, 
are collected like so many small veins into one 
or more trunks, called the vasa efferentia of the 
gland ; not unfrequently there is but one of 
these vessels passing from a gland, and rarely 
more than two or three; they are, however, 
generally larger than the vasa inferentia, and often 
double theirsize. ( Fig. 52.) A similararrange- 
ment in the bloodvessels before entering or 
passing from their agen glandular organs 
may be noticed in the spleen and kidney, but 
the only instance in which a bloodvessel col- 
lecting its contents from branches assumes 
the opposite function of distributing them 
into narrow streams occurs in the vena porta, 
‘where the blood is to be passed through 
the liver to be subjected to its action. The 
same object, it is true, is effected at the heart 
with the blood of the vene cave, together with 
the lymph and chyle, when conveyed in capil- 
lary streams through the lungs to be converted 
into arterial blood; the right side of the heart, 
however, here intervenes between the collect- 
ing vessels and those which have to redistribute 
the blood ; the latter also are called arteries 
though they convey the same venous blood to 
the lungs which the former vessels brought to 
the heart. 
The vasa inferentia are by most authors des- 
cribed as entering that edge of the gland which 
is farthest removed from the trunks of the 
system, and the vasa efferentia that nearest 
tothem. This I find not to be the case; the 
vessels usually plunge into and emerge from 
the broadest surfaces of the gland; sometimes 
it is the deeper surface, sometimes the more 
superficial, and frequently both. The vasa in- 
ferentia may enter one surface, and the vasa 
efferentia pass from the same or the opposite 
surface of the gland. The vasa efferentia, as 
they proceed onward, become the vasa infe- 
rentia of succeeding glands; thus the lymph is 
often made to traverse several glands before it 
is received by the trunks of the system. This 
is so much the case in the neighbourhood of 
the thoracic duct, especially in the pelvic and 
abdominal cavities, that the lymphatic system 
assumes altogether a different aspect; the net- 
work appearance, the uniformity in point of size, 
are lost sight of in the numerous large short 
vasa efferentia and inferentia, intervening be- 
tween the closely set glands. The appropriate 
lymphatic vessels of the viscera and walls of 
these cavities, nevertheless maintain the ordi- 
nary disposition, the appareut irregularity de- 
nding upon the circumstance, that the large 
ymphatics of the lower extremities, are inter- 
rupted by numerous glands in their passage to 
the thoracic duct. 
The lymphatic vessels are distributed through- 
out the body on two planes, one superficial, the 
LYMPHATIC AND LACTEAL SYSTEM. 
other deeply seated. The vessels of the t 
planes where they approach each other cc - 
nicate freely. A similar arrangement takes p 
partially in the venous system ; and it is inter 
ing to remark that where this occurs, the. 
like the lymphatics, are armed with valves. We 
cannot fail to recognize here a double pr 
vision to facilitate the progress of the cont 
of a vessel towards their proper destinati 
while the valves prevent effectually any retro. 
grade movement, the double plane of vessel: 
by increasing the number of channels, le ser 
the liability to arrest from the various cau 
of obstruction. The superficial lymphatis 
accompany more or less the superficial vein 
where these occur, but in other parts of @ 
body they assume various appearances pecul 
to each viscus or organ ; the superficial lymph 
tics, of the liver, spleen, kidney, and lung 
instance, differ materially from each oth 
arrangement and appearance. The deep 
lymphatics every where follow the course of 
large bloodvessels. They are fewer in 
and perhaps rather larger than the superficia 
The superficial and deep lymphatics commu 
nicate with each other in the lymphatic glas 
as well as in different parts of their course. 
The chief peculiarity of the coats of 
lymphatic vessels is their remarkable thinne 
and transparency ; in other amps they be: 
considerable resemblance to the coats of tl 
veins ; indeed in some of the lower animals 
veins are nearly as thin, and when empt 
blood, as transparent as the lymphatics. A 
anatomists admit the existence of two coats 
the lymphatics, an internal serous lining, 
at intervals is thrown into folds to form thy 
valves, and an external thicker fibrous covering; 
to these is added by some anatomists, with whor 
I am disposed to coincide, a third, anale 
to the cellular tunic of the bloodvessels, . 
conveys to them their vasa vasorum, and by 
which they are connected to the surrounding 
Structures. 
The inner tunic is extremely fine and delic 
probably less elastic and extensible than is 
nerally imagined, and is the first to give 
under distention from forced injections. — 
appears to possess a much closer texture th 
the fibrous tunic, to which it is firmly adhe: 
and whose contractions and dilatations i 
compelled to follow. The epithelium 
are distinguished with difficulty on the inne 
surface of this tunic, but I have satisfied my 
self of their existence. On placing an open 
lymphatic in the field of the microscope 
the bloodvessels have been minutely injec 
the vasa vasorum may be very distinctly seen 
but it is difficult, from the perfect trans 
parency, of this tunic, to say whether t 
vessels reach it, or are only seen through 
The vasa vasorum of the lymphatics do 
appear to affect any constant or fixed arr 
ment; they are by no means numerous, and [ 
have never been able to detect any on the val- 
vular folds. | 
The fibrous tunic, like the internal, 1s trans 
parent; it is very elastic, and admits of consi- 
derable distention without rupture. There is 
4 
Be? 
it 
