934 



HUMAN ANATOMY. 



The mucous membranes have essentially the same arrangement, the net-work with- 

 in the small intestine, for instance, being arranged in two more or less distinct layers, one 

 of which lies in the submucosa and sends loops or blindly ending processes into the villi, 

 while the other is situated in the muscular coat. What may be regarded as a third net- 

 work, lying beneath the serous or connective-tissue investment, is formed by the anas- 

 tomosis of the stems arising from the deeper net-works and it is from this last net-work 

 that the eflierent stems arise. In most other organs lined by mucous membrane a 

 similar arrangement occurs, although in the uterus, bladder, and ureters the submucous 

 net-work seems to be wanting, the muscular set alone being demonstrable. Through- 

 out the serous membranes the net-works possess naturally a layered arrangement, but 

 in the more massive organs, such as the liver and pancreas, they are arranged with 

 reference to the constituent lobules, each being invested by an interlobular net-work. 

 Considerable variation exists in the closeness of the net-work in different organs, 

 and, indeed, in different parts of the same organ, but everywhere the lymph- 

 capillaries are exceedingly thin-walled and possess no valves. As has been pointed 

 out, the view formerly prevailed that the capillaries communicated directly with the 

 great serous cavities of the body, with the spaces of the connective tissues, and even 

 with the pericellular spaces which occur in the more compact tissues, all these being 

 regarded as radicles of the lymphatic vessels. It is now believed, however, that 

 such is not the case, but that the net-works, which are everywhere continuous, are 

 completely closed except for their communications with the efferent vessels. 



The Lymph-Vessels. — The lymph-vessels, 

 which issue from the capillary net-works and convey 

 the lymph ultimately to the subclavian veins, have 

 an arrangement closely resembling that of the veins, 

 and, indeed, the larger ones are usually situated 

 alongside and accompany the course of blood-vessels. 

 Just as it is possible over the surface of the body and 

 limbs to distinguish between superficial and deep 

 veins, so there can be recognized a siipcfficial set 

 of lymphatic vessels (vasa lymphatica superficialia), 

 situated superficially to the fascia which encloses the 

 musculature, and a deep set (vasa lymphatica profunda), 

 the vessels of which lie beneath the fascia ; numerous 

 communications, however, exist between the two sets. 

 Just as the veins unite to form larger trunks 

 as they pass from the capillaries toward their termi- 

 nation, so, too, the lymphatics ; but the latter 

 present two peculiarities which distinguish them 

 from the veins. They do not anastomose as abun- 

 dantly as the latter and there is not the same 

 proportional increase in the size of a lymphatic 

 vessel formed by the junction of others as in the 

 veins, so that, while the lymphatics at their origin 

 from the capillary net-works may have the same 

 calibre as the corresponding veins, yet their terminal 

 trunks are of much smaller diameter. 



As a rule, several lymphatic vessels arise from 

 the capillary net-work of any organ or region of the 

 body, and, since the net-work is to be regarded as 

 practically continuous over large areas, it would 

 appear that the flow of lymph from any circumscribed 

 area might take place through widely separated 

 stems and be carried along very different paths. 

 And such, to a certain extent, is the case ; but it 

 has been found by experiment and by the observation 

 of pathological conditions that for each organ or region there is a more or less definite 

 lymphatic path, each vessel or group of vessels tending to drain a somewhat definite 

 area of the net-work, a fact of considerable importance from the diagnostic standpoint. 



Shaded part of figure shows area 

 drained by right lymphatic duct; lym- 



i)hatics of remaining territory received 

 )y thoracic duct. 



