210 



LYMPHATIC AND LACTEAL SYSTEM. 



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 



Fig. 48. 



a, b, and c, lymphatic vessels inverted, giving three 

 different mews 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 is 

 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 pre-ents 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, a front view of a valvular flap, b, a profile 

 view of a lymphatic vessel and valvular flap j 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 

 portion, of the lining membrane only. (From 

 Breschet.) 



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 " Systeme 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 



a doubling of the lining membrane only, while 

 the thicker part, near the base, he has assured 

 himself is produced by a prolongation which 

 the fibrous coat sends inwards between the 

 folds of the inner tunic. I have not been able 

 to verify this description of the structure of the 

 valve, but I have distinctly observed circular 

 constrictions in the more bead-like lymphatics 

 seen in the neighbourhood of some of the 

 lymphatic glands, into the formation of which 

 the fibrous coat does appear to enter. On 

 laying open one of these vessels previously 

 distended with quicksilver and dried, opposite 

 the external constrictions, which were numerous, 

 and not more than a line apart, valvular folds, 

 differing from those hitherto described, were 

 seen to project into the interior of the vessel ; 

 they did not completely close its cavity, but 

 left a circular or oval opening, through which 

 the contents of the vessel might pass in either 

 direction. These valvular constrictions re- 

 sembled much the dried pyloric valve (Jig. 50, 

 B) ; and I am inclined to believe, from their 

 thickness, that they contain circular fibres de- 

 rived from the middle coat, by which during 

 life they may be able to close their vessels as 

 perfectly as the pyloric valve closes the com- 

 munication between the stomach and duode- 

 num. In very many places there occur two 

 semilunar folds (fig. 50, A), apparently formed 

 of the lining membrane only, like the flaps of 

 the ordinary valves, from which they differ, how- 

 ever, in having their attached and unattached 

 edges, as well as the flaps themselves, on the 

 same plane, consequently not forming pouches, 

 but a transverse though incomplete septum 

 across the vessel. Each of these flaps extends 

 only one-third across the vessel, and terminates 

 by a crescentic edge, by which arrangement an 

 elliptical opening is left in the central third of 

 the vessel, between the two folds. This form 

 of valve would appear to offer a partial obstruc- 

 tion to the passage of the lymph in either direc- 

 tion, as no provision is manifest by which these 

 flaps would be made to fall against the sides 

 of the vessel, either by the onward or retrograde 

 course of its contents. I have frequently no- 

 ticed a combination of the circular constriction 

 witli the semilunar flaps here described (fig. 50, 

 C), by which mechanism, supposing the former 

 to be endowed with a vital contractility, the 

 latter might be brought in contact, so as com- 

 pletely to close the elliptical opening that would 

 otherwise be left in the centre of the vessel. 



At the entrance of the lateral branches into 

 the thoracic duct, or of one lymphatic into ano- 

 ther, a valve will be found, of a somewhat diffe- 

 rent form to those already described. It is com- 

 posed oftwosemilunarflaps, seldom of equal size, 

 arranged somewhat like the ilio-ccecal valve. 

 One flap is occasionally so slightly developed 

 that there appears but one large semilunar fold 

 at the entrance of the vessel. At the union of 

 some of these vessels with others, especially of 

 those which lie nearly parallel with each other, 

 no valve will be found, but simply a defined 

 curved line, marking the orifice of communica- 

 tion. The valves in the lymphatic system are 

 very closely set together. The distance be- 

 tween them varies much. In vessels of a line 



