226 



THE CIRCULATORY SYSTEM 



[CH. XIX. 



Chyle is lymph containing finely divided fat-globules. In some parts 

 of its course the lymph-stream passes through lymphatic glands, to 

 be described later on. 



Origin of Lymph Capillaries. The lymphatic capillaries com- 

 mence most commonly either (a) in closely-meshed networks (see 

 fig. 210), or (&) in irregular lacunar spaces, lined by endothelium, 

 between the various structures of which the different organs are 

 composed. These spaces freely communicate with the cell spaces 

 (Saft Kanalchen, see p. 31) of the tissues. 



FIG. 210. Lymphatics of central tendon of rabbit's diaphragm, stained with silver nitrate. The 

 shaded background is composed of bundles of white fibres, between which the lymphatics lie. 

 I, Lymphatics lined by long narrow endothelial cells, and showing v valves at frequent intervals. 

 (Schofield.) 



The lacteals offer an illustration of another mode of origin, 

 namely, as blind dilated extremities in the villi of the small intestine 

 (see fig. 28, p. 22). 



The structure of lymphatic capillaries is very similar to that 

 of blood capillaries ; their walls consist of a single layer of elongated 

 endothelial cells with sinuous outline, which cohere along their edges 

 to form a delicate membrane. They differ from blood capillaries 

 mainly in their larger and very variable calibre, in the presence of valves, 

 and in their numerous communications with the spaces of the tissues. 



In certain parts of the body, stomata exist, by which lymphatic 

 capillaries directly communicate with parts formerly supposed to be 

 closed cavities. They have been found in many serous membranes ; 

 a serous cavity thus forms a large lymph-sinus or widening out of 

 the lymph-capillary system with which it directly communicates. 



