MINUTE ANATOMY OF THE CAPILLARY LYMPHATICS. 301 



perfectly demonstrated in the lymphatics, and that only the 

 general relations existing between the structure of any organ and 

 its lymphatics present characteristic features. The varieties that 

 occur in the arrangement of the lymphatics exhibit many pecu- 

 liarities in certain regions of the smaller lymph vessels. Thus we 

 see, in parts where they are very numerous and closely arranged, 

 there are not unfrequently lacunar spaces even in Mammals, 

 as if they had coalesced to form a flat and wide vessel; we meet 

 also with a pair of lymph tubes accompanying a bloodvessel, and 

 not unfrequently with regular sheaths, which partially or en- 

 tirely surround them, as, for example, in the case of the chyle 

 vessels in the mesentery of the Mouse (Briicke). In such in- 

 stances as these we recognise in Mammals arrangements essen- 

 tially similar to the lymph sacs of Amphibia. 



There is still another circumstance that becomes intelligible 

 from this comparison if we remember that certain sections of 

 the lymphatic system of the Amphibia do not possess a tubular 

 form, but represent ensheathing or lacunar spaces. They are 

 thus analogous, as we have already seen, to serous sacs, and it 

 will be understood how the latter stand in immediate relation 

 with the lymphatic system, are in direct communication with 

 it, and possess similar contents (see infra). 



This variability of form recurs in the narrowest section of the 

 lymphatic system, that is to say ; in the lymphatic capillaries. 

 For even amongst Mammals we meet in certain organs with 

 lacunae, representing the roots of the lymphatics ; whilst in Am- 

 phibia the great majority of the lymph capillaries are tubular. 

 The lacunse correspond in form with the spaces between the parts 

 of the organs they invest, such as the ducts of glands, etc. The 

 capillary tubes, even in their finest branches, are provided with 

 varicose enlargements, and these are often situated at the points 

 of junction of the vessels, and occur so suddenly that trans- 

 verse processes project into the lumen of the vessel, which are 

 again so placed that they form a kind of valve. Such dila- 

 tations often succeed one another at very short intervals, 

 especially in those lymphatics which immediately follow the 

 capillaries, giving the impression of tubes constructed of a 

 series of Florence flasks, of which each is inserted by its neck 

 into the base of the one preceding it (see fig. 57). It is easy to 



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