984 
near to large veins covered by strong cartilages, 
which resemble our clavicles, and which there- 
fore may be called subclavian veins. Towards 
these all the lymphatic vessels of the body are 
directed, the lymphatics of the kidneys and 
organs of generation with those of the tail and 
inferior parts ascending, those of the flesh and 
side fins of the trunk of the body running in- 
wards, and those of the superior parts and of 
the brain, organs of the senses, heart, and gills, 
descending. 
The branches ofthe lymphatic vessels form 
larger angles where they terminate in their 
trunks than are found in the veins, and the 
smaller branches are connected by transverse 
canals. The large lymphatics of the muscular 
organs, near their joining with the lacteals, are 
collected together in the most simple manner, 
without forming such intricate plexuses as are 
found in the course and near to the termination 
of the lactea! vessels: the lymph from the 
head and thorax in particular is conveyed 
chiefly by a single trunk, which receives large 
lateral branches from the adjacent parts. At last 
a single vessel on each side of the fish, and in 
which there is no dilatation or large receptacle, 
receives all the chyle and lymph, and terminates 
in the subclavian vein of the corresponding 
side very near its junction with the internal 
jugular vein, or nearly in the angle which these 
two vessels form by their joining. The blood is 
poe from getting into these two vessels 
y : pair of valves placed at the termination of 
each. 
In the osseous Fishes the course of the 
lymphatics has been traced both by Monro and 
Hewson,* principally in the Gadide and the 
Salmon: their general arrangement has been 
described above. 
Four lymphatic vessels which terminate in 
the subclavian receptacles chiefly merit attention. 
The first conveys the lymph from the ventral pa- 
rietes, from the ventral and pectoral fins,and from 
the heart. The second runs up the side of the 
fish parallel to the great mucous duct, and brings 
the lymph from the principal muscles of the 
tail and body. The third is deep-seated and 
conveys the lymph from the se spinal me- 
dulla, and upper part of the head, while the 
fourth lymphatic vessel, or rather plexus of ves- 
sels, brings the lymph from the brain and organs 
of the ’sensés, and from the mouth, jaws, and 
gills. 
The two receptacles into which all these ves- 
sels open communicate freely with each other 
by wide canals, which: pass chiefly behind the 
heart and cesophagus, and each ultimately 
empties itself into the upper end of its corre- 
sponding vena cava inferior, contiguous to the 
termination of the internal jugular vein, the 
communications between the lymphatic and 
venous systems being guarded by valves. 
It will be seen from the above description that 
the lymphatic system of Fishes offers several 
remarkable peculiarities when compared with 
what is met with among the ah ge ertebrata, 
amongst which may be noticed the total want 
* Phil. Trans. for 1769. 
PISCES. a" 
of lymphatic glands, and the absence of valves 
in the absorbent trunks. Owing to this latter 
circumstance, nothing is more easy than to in- 
ject them from trunk to branch, and thus dis- 
play their minute ramifications with the greatest 
ease. In this manner Mr. Hewson detected in 
the Cod a beautiful net-work of lymphatic — 
vessels situated between the muscular and vil- 
lous coats of the intestine, something analogous _ 
to what exists in the Turtle; but in Fish it is 
more evident that there can be no deception, — 
seeing that the injection is contained in cylin- 
drical vessels, not diffused in cells, as is the — 
case in the reptile. If mercury be injected — 
into this ne th it spreads ei in sien 
and if the intestine inverted and sli 
pressed, it can readily be seen to pass into the 
villi of the intestinal mucous membrane. In 
the stomach, however, the absorbents have a 
different arrangement. When minutely in- 
jected with mercury, they are seen to pass 
through the external coats, dividing into smaller — 
and smaller bratiches, without any appearance — 
of a net-work between the muscular and the 
villous coat, so that the absorbent vessels of the 
stomach manifestly exhibit a different arrange- 
ment from those of the intestine. 
By adopting a similar mode of injecting from — 
trunk to branch, Dr. Monro succeeded in de- 
monstrating numberless lymphatics in the brain, 
eye, ear, and nose, in all of which organs their 
existence had been previously doubted; and, 
also, in proving that their ramifications in 
the rest of the body were far more extensive 
than had been supposed. He, moreover, points 
out another circumstance of considerable im- 
portance in a physiological point of view, viz., 
+ 
that on examining the minute branches of the 
lymphatics, they are found to consist of an im. 
mense number of anastomosing canals, many 
of which enter the neighbouring lymphaties a 
right angles instead of being di owards 
the heart, by which means a net-work is pr 
duced so very intricate that, when a small por 
tion only is examined, it is difficult or next 
impossible to ascertain what has been t 
natural course of the lymph; it is therefo 
evident that, from the great number and un 
vourable direction of these canals, general pr 
sure cannot in this case be a chief cause of 
progressive motion of the lymph, but that ea 
vessel must contribute to its progress by a we 
regulated action. a 
Another remarkable circumstance is 
by Monro in connection with the lymp 
vessels, namely, that in the Skate they ¢ 
by patulous orifices situated upon the back | 
the Fish, of sufficient size to allow not only ; 
but water, milk, quicksilver, and even oil 
turpentine coloured with vermilion, to be 
charged upon the surface of the skin, ev 
when the force employed in injecting t 
fluids was very slight, and no extravasa 
produced into the cellular tissue either un 
the skin or in the muscular interstices. 
function attributed to these open vessé 
Monro is, however, even if they exist, 
hypothetical, namely, that they are for the 
purpose of absorbing from the ocean the fluic 
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