210 
simply presses the flaps back against the sides 
of the vessel, and thus no obstruction is offered 
to its onward course. The flap of a valve con- 
sists of a fold of the inner coat of the vessel, 
which, where a valve is to be formed, ceases to 
a, b, and c, lymphatic vessels inverted, giving three 
different views of the valves formed by the lining 
membrane. (After Breschet. ) 
line the vessel, and is reflected towards its inte- 
rior; having reached half-way across, it 1s 
doubled upon itself, and returns to the side of 
the vessel, which it continues to line as if it 
had never been interrupted. The two layers 
of this fold adhere very firmly together so as to 
form a very delicate transparent semilunar flap. 
It presents a convex attached, and a straight or 
slightly concave unattached edge; the former 
corresponds to a semilunar line on the interior 
of the vessel, the horns of which look towards 
the trunks of the system, where the lining mem- 
brane was reflected from and returned to the side 
of the vessel; the latter to the line of doubling 
Fig. 49. 
a, afront view of a valvular flap. 5, a profile 
view of a lymphatic vessel and valvular fap; the 
lower half of the flap, or that nearest the base, 
is represented thicker than the rest. According 
to Lauth and Breschet, this thicker portion is 
formed of all the coats of the vessels ; the thinner 
ortion, of the lining membrane only. (From 
eschet. ) 
of the membrane upon itself; thus a little pouch 
is formed between the flap and the side of the 
vessel, which can only be filled by the fluid 
passing in one direction ; and as a valve is 
constituted of two such pouches, when they are 
filled the vessel is completely closed. Some 
anatomists conceive that a lamina of fibrous 
tissue intervenes between the layers of the fold. 
Breschet, in his “Systéme Lymphatique,” 
adopts Lauth’s view of the structure of the 
valve. He describes the flap of a valve as 
composed of two parts, one thicker and situated 
at the base of the fold, the other forming the 
rest of the flap more thin and delicate. It is 
this latter part which he conceives is formed by 
LYMPHATIC AND LACTEAL SYSTEM. 
a doubling of the lining membrane only, whil 
7 thicker part, vay Me e base, he has assured 
imself is produced a prolongati tich 
the Shrous coat anak inwards betwen he 
folds of the innertunic. TI have not been able 
to — this description of the structare of the 
valve, but I have distinctly observed circulat 
constrictions in the more bead-like lymphatic 
seen in the neighbourhood of some of the 
K bynes glands, into the formation of whic 
the fibrous coat does appear to enter. Of 
laying open one of these vessels previous 
distended with quicksilver and dried, opposit 
the external constrictions, which were numerow 
and not more than a line apart, valvular fo 
differing from those hitherto described, wer 
seen to project into the interior of the vessel 
they did not completely close its cavity, bw 
left a circular or oval opening, through whie 
the contents of the vessel might pass in eith 
direction. These valvular constrictions 1 
sembled much the dried pyloric valve (fig. 5 
B); and I am inclined to believe, from th 
thickness, that they contain circular fibres de 
rived from the middle coat, by which durin 
life they may be able to close their vessels” 
perfectly as the pyloric valve closes the cot 
munication between the stomach and duc 
num. In very many places there occur t 
semilunar folds (fig. 50, A), mI fer orm: 
of the lining intial only, like the flaps 
the ordinary valves, from which they differ, hoy 
ever, in having their attached and unattach 
edges, as well as the flaps themselves, on 
same plane, consequently not forming pouches 
but a transverse though incomplete septt 
across the vessel. Each of these flaps extem 
only one-third across the vessel, and terminat 
by a crescentic edge, by which arrangement a 
elliptical opening is left in the central third 
a vessel, between the two folds. This fort 
of valve would appear to offer a partial obstrue 
tion to the tr of the lymph in either din 
tion, as no provision is manifest by which th 
flaps would be made to fall against the sid 
of the vessel, either by the onward or retrogr 
course of its contents. I have 
ticed a combination of the circular constrict 
with the semilunar flaps here described (fig-5 
C), by which mechanism, supposing the form 
to be endowed with a vital contractility, t 
latter might be brought in contact, so as Ci 
pletely to close the elliptical opening that wo 
otherwise be left in the centre of the vessel. 
At the entrance of the lateral branches i 
the thoracic duct, or of one lymphatic into ar 
ther, a valve will be found, of a somewhat dif 
rent form to those already described. It is con 
posed oftwo semilunar flaps, seldom of equal 
arranged somewhat like the ilio-ceecal 
One flap is occasionally so slightly devele 
that there appears but one large semilunar fo 
at the entrance of the vessel. At the uniono 
some of these vessels with others, especially o 
those which lie nearly = with each other 
no valve will be found, but simply a defini 
curved line, marking the orifice of commu 
tion. The valves in the lymphatic system 
very closely set together. The distane 
tween them varies much. In vessels of a line 
equently nD 
