LYMPHATIC AND LACTEAL SYSTEM. 
great variety of opinion with respect to the na- 
ture of its tissue. Breschet and many other 
anatomists describe this tunic as resembling 
the cellular coat of the bloodvessels, and are 
under the impression that the lymphatics are 
altogether deficient in that which is analogous 
to the middle or fibrous coat of the arteries and 
veins. Mascagni and Rudophi have not been 
able to detect muscular fibres in it. Cruveilhier 
conceives it to be composed of the tissu jaune 
elastique, or tissu dartoide. Schreger thinks he 
has seen circular muscular fibres in the thoracic 
duct of manand of large animals, and Sheldon 
States that he has distinctly seen muscular 
fibres in the thoracic duct of the horse. By 
lacing a portion of the thoracic duct or large 
ymphatic laid open with the lining membrane 
uppermost, on a piece of glass, and by scra- 
ping off the internal membrane, the fibrous 
tunic will be exposed ; if it be now moistened 
with a drop of water, and a piece of tale placed 
over it, it may be readily examined under the 
microscope. I have several times examined 
rtions of the thoracic duct and of the larger 
ymphatics taken from the horse, and from the 
human subject, and have invariably found the 
tunic exposed on’ removing the lining mem- 
brane, to be composed of fibres passing princi- 
pally in the longitudinal direction ; these fibres 
are uniform and cylindrical, and resemble in 
these respects the organic muscular fibre as de- 
scribed by Schwann ; they lie for the most part 
parallel with each other, and are occasionally 
seen to form a large fasciculus, somewhat analo- 
gous to the longitudinal muscular bands of the 
large intestine. These fibres measure from 
1-5000th to 1-6000th of an inch in diameter, 
_ and present at intervals, a sudden zigzag inflec- 
tion ; several fibres collected together into a sort 
of primitive fasciculus are bent together at the 
same points. These abrupt deviations from 
the straight line do not occur at equidistant 
points ; the intervals between them differ 
greatly 5 they average 1-400th of an inch in 
ength. Under the lining membrane some few 
fibres may be distinguished taking a transverse 
course, others may be seen in an oblique direc- 
tion, but the great majority are arranged longi- 
tudinally. The primitive fibre of cellular 
tissue is freely mixed with the peculiar fibres 
just described. The physiological fact that the 
lymphatics have the power of contracting and 
emptying themselves of their contents, has not 
been disputed ; but with respect to the nature 
and form of the fibre in virtue of which they 
possess this faculty, there has been and still 
exists great uncertainty. No one can have ex- 
amined the lacteal or lymphatic vessels in a 
recently killed animal without having observed 
the rapidity with which this system will empty 
itself of the fluid it contains ; and if the trunk 
of the system be ligatured, it will be found 
that this power remains for an hour or more 
after death, as may be proved by puncturing 
the duct within this period below the ligature, 
or by puncturing a distended lymphatic, which 
will be instantly evacuated of its contents, and 
will refill again and again when pressure is 
made below the orifice. 
Lymph hearts——I must not here omit to al- 
VOL. III. 
209 
lude to the pulsatile sacs or hearts belonging to 
the lymphatic system, discovered by Miller in 
frogs, toads, salamanders, and lizards, and by 
Panizza in serpents. In frogs, Miiller describes 
two pairs, one situated just under the skin in 
the ischiadic region, the other more deepty 
seated over the third cervical vertebra. Their 
pulsations he describes as about 60 in a 
minute and not synchronous with those of the 
heart. The lower pair propel the lymph into 
the ischiadic vein ; the upper, into the internal 
jugular.* Ihave seen these transparent pul- 
sating bodies in the frog, where they may be 
easily exposed by removing the skin from 
either side of the rudimentary tail, but have 
not examined them sufficiently to pass any opi- 
nion upon them. 
External to the fibrous tunic is situated a 
delicate and loose cellular tissue, which per- 
forms the same offices for the lymphatic, which 
the cellular tunic does for the artery and vein, 
viz. it conveys to it the vasa vasorum for its nu- 
trition, and connects it to the surrounding tis- 
sues. The supply of nerve to the lymphatic 
has not hitherto been detected ; there can how- 
ever be no doubt but that it possesses its proper 
degree of sensibility, and its contractile power 
is in all probability regulated by nerve. 
Fig. 47. 
a and b, lymphatics laid open longitudinally to shew 
the arrangement of the valves in their intericrs. 
( After Breschet. ) 
The valves of the lymphatics resemble in 
their mode of formation and in their appear- 
ance the same structures in the veins; they are 
however more frequent and more universal in 
the lymphatic system ; indeed, in the more per- 
fect animals they are found every where except 
in the incipient networks of this system. It 
has already been stated that in fishes and in 
some amphibious animals the lymphatic system 
is either entirely deficient in valves, or is only 
supplied with them in a partially developed 
state. The valve is composed of two semi- 
lunar flaps, so arranged that the reflux of 
the fluid within, forces them away from the 
sides of the vessel towards its centre, where 
the two flaps meet and completely close it, 
while the fluid passing in its proper direction 
* Professor Weber has described one of these 
hearts in a large serpent, the pithon bivitatus. It 
measured nine lines in length, and four in breadth ; 
it had an external cellular, a middle muscular, and 
an internal serous tunic. See Phil. Trans 1833, 
Miiller’s Archiv. for 1835, and Valentin’s Reper- 
torium, Bd: 1, p. 294. [Miiller has subsequently 
described similar lymphatic hearts in the Chelonian 
Reptiles, Archiv. 1840, p. 1-4.—ED.] 
Pp 
