208 



LYMPHATIC AND LACTEAL SYSTEM. 



more than five or six. They maintain their ordi- 

 nary size and appearance to within a quarter of 

 an inch of the gland, where they suddenly branch 

 out, artery-like, into several exceedingly minute 

 vessels which plunge into the gland, thus con- 

 veying the lymph, in a minutely divided state 

 through this organ to emerge again from it by 

 a converse arrangement of equally small vessels, 

 which at a quarter of an inch from the gland, 

 are collected like so many small veins into one 

 or more trunks, called the vusu efferent ia of the 

 gland ; not unfrequently there is but one of 

 these vessels passing from a gland, and rarely 

 more than two or three; they are, however, 

 generally larger than the vasainferentia, and often 

 double theirsize. (Fig. 52.) A similar arrange- 

 ment in the bloodvessels before entering or 

 passing from their appropriate glandular organs 

 may be noticed in the spleen and kidney, but 

 the only instance in which a bloodvessel col- 

 lecting its contents from branches assumes 

 the opposite function of distributing them 

 into narrow streams occurs in the vena porta, 

 where the blood is to be passed through 

 the liver to be subjected to its action. The 

 same object, it is true, is effected at the heart 

 with the blood of the venae cavse, together with 

 the lymph and chyle, when conveyed in capil- 

 lary streams through the lungs to be converted 

 into arterial blood ; the right side of the heart, 

 however, here intervenes between the collect- 

 ing vessels and those which have to redistribute 

 the blood ; the latter also are called arteries 

 though they convey the same venous blood to 

 the lungs which the former vessels brought to 

 the heart. 



The vasa inferentia are by most authors des- 

 cribed as entering that edge of the gland which 

 is farthest removed from the trunks of the 

 system, and the vasa efferentia that nearest 

 to them. This I find not to be the case; the 

 vessels usually plunge into and emerge from 

 the broadest surfaces of the gland ; sometimes 

 it is the deeper surface, sometimes the more 

 superficial, and frequently both. The vasa in- 

 ferentia may enter one surface, and the vasa 

 efferentia pass from the same or the opposite 

 surface of the gland. The vasa efferentia, as 

 they proceed onward, become the vasa infe- 

 rentia of succeeding glands ; thus the lymph is 

 often made to traverse several glands before it 

 is received by the trunks of the system. This 

 is so much the case in the neighbourhood of 

 the thoracic duct, especially in the pelvic and 

 abdominal cavities, that the lymphatic system 

 assumes altogether a different aspect; the net- 

 work appearance, the uniformity in point of size, 

 are lost sight of in the numerous large short 

 vasa efferentia and inferentia, intervening be- 

 tween the closely set glands. The appropriate 

 lymphatic vessels of the viscera and walls of 

 these cavities, nevertheless maintain the ordi- 

 nary disposition, the apparent irregularity de- 

 pending upon the circumstance, that the large 

 lymphatics of the lower extremities, are inter- 

 rupted by numerous glands in their passage to 

 the thoracic duct. 



The lymphatic vessels are distributed through- 

 out the body on two planes, one superficial, the 



other deeply seated. The vessels of the two 

 planes where they approach each other commu- 

 nicate freely. A similar arrangement takes place 

 partially in the venous system ; and it is interest- 

 ing to remark that where this occurs, the veins, 

 like the lymphatics, are armed with valves. We 

 cannot fail to recognize here a double pro- 

 vision to facilitate the progress of the contents 

 of a vessel towards their proper destination ; 

 while the valves prevent effectually any retro- 

 grade movement, the double plane of vessels, 

 by increasing the number of channels, lessens 

 the liability to arrest from the various causes 

 of obstruction. The superficial lymphatics 

 accompany more or less the superficial veins 

 where these occur, but in other parts of the 

 body they assume various appearances peculiar 

 to each viscus or organ ; the superficial lympha- 

 tics, of the liver, spleen, kidney, and lungs, for 

 instance, differ materially from each other in 

 arrangement and appearance. The deep-seated 

 lymphatics every where follow the course of the 

 large bloodvessels. They are fewer in number 

 and perhaps rather larger than the superficial. 

 The superficial and deep lymphatics commu- 

 nicate with each other in the lymphatic glands 

 as well as in different parts of their course. 



The chief peculiarity of the coats of the 

 lymphatic vessels is their remarkable thinness 

 and transparency ; in other respects they bear 

 considerable resemblance to the coats of the 

 veins ; indeed in some of the lower animals the 

 veins are nearly as thin, and when empty of 

 blood, as transparent as the lymphatics. All 

 anatomists admit the existence of two coats in 

 the lymphatics, an internal serous lining, which 

 at intervals is thrown into folds to form the 

 valves, and an external thicker fibrous covering; 

 to these is added by some anatomists, with w horn 

 I am disposed to coincide, a third, analogous 

 to the cellular tunic of the bloodvessels, which 

 conveys to them their vasa vasorum, and by 

 which they are connected to the surrounding 

 structures. 



The inner tunic is extremely fine and delicate, 

 probably less elastic and extensible than is ge- 

 nerally imagined, and is the first to give way 

 under distention from forced injections. It 

 appears to possess a much closer texture than 

 the fibrous tunic, to which it is firmly adherent, 

 and whose contractions and dilatations it is 

 compelled to follow. The epithelium scales 

 are distinguished with difficulty on the inner 

 surface of this tunic, but I have satisfied my- 

 self of their existence. On placing an opened 

 lymphatic in the field of the microscope after 

 the bloodvessels have been minutely injected, 

 the vasa vasorum may be very distinctly seen ; 

 but it is difficult, from the perfect trans- 

 parency of this tunic, to say whether these 

 vessels reach it, or are only seen through it. 

 The vasa vasorum of the lymphatics do not 

 appear to affect any constant or fixed arrange- 

 ment; they are by no means numerous, and I 

 have never been able to detect any on the val- 

 vular folds. 



The fibrous tunic, like the internal, is trans- 

 parent; it is very elastic, and admits of consi- 

 derable distention without rupture. There is 



