LYMPHATIC AND LACTEAL SYSTEM. 



209 



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 man and of large animals, and Sheldon 

 states that he has distinctly seen muscular 

 fibres in the thoracic duct of the horse. By 

 placing a portion of the thoracic duct or large 

 lymphatic 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 talc placed 

 over it, it may be readily examined under the 

 microscope. I have several times examined 

 portions of the thoracic duct and of the larger 

 lymphatics 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 

 l-5000th to l-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; they average l-400th of an inch in 

 length. 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 whicli 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. nr. 



lude to the pulsatile sacs or hearts belonging to 

 the lymphatic system, discovered by Miiller 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 deeply 

 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.* I have seen these transparent pul- 

 sating bodies in the frog, where they maybe 

 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 ad b, lymphatics laid open longitudinally to shew 

 the arrangement of the valves in their interiors. 

 (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 i* only 

 supplied with them in a partially developed 

 state. The valve is composed of tsvo 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 pilhon 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, 

 Mailer's Archiv. for 1835, and Valentin's Reper- 

 torium, Bd. 1, p. '294. [Miiller has subsequently 

 described similar lymphatic hearts in the Chelonitm 

 Reptiles. Archiv! 1840, p. 1-4. KD.] 



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