the twig supplying the convolution ; c, glo- 



TISSUES OF THE BODY. 373 



It is easy to conceive also that eacli form of network may make its 

 appearance with ever so many different modifications. 



On account, for instance, of the narrowness of the space in such conical 

 protuberances as the sensitive papillae of the skin and papillae of the mucous 

 membranes, regular capillary loops, as they are called, may be formed 

 (fig. 368). Again, if these cones attain much greater dimensions, as in 

 the villi of the small intestines, an arrangement of capillaries is brought 

 about which is known under the name of the loop network, a further 

 complication of the former. Tn this 

 case we see, passing between the two 

 or more principal vessels of the sling, 

 a finer set of tubes holding a trans- 

 verse course (fig. 369, b). 



Finally, in this sketch may be in- 

 cluded the glomerulus, as it is called, 

 of the kidney, an arrangement of 

 vessels peculiar to, and characteristic 

 of, that organ (fig. 370). Here we find 

 a minute arterial twig (6), micro- 

 scopically small indeed, suddenly 

 curled upon itself in a manner 

 similar to the inferior portion of a 

 sweat gland (c). . Within the con- 



VOlutlOll it may divide into branches 



to a certain extent, as in man and the 



mammalia, or remain single, after fc ff; H urinary tubules. 



which an efferent vessel makes its appearance (d\ which, at a short 



distance from the glomerulus is resolved into a capillary network (ef). 



206. 



The lymphatic system is an appendage of the circulatory, designed to 

 bear back into the blood those nutritive fluids, impregnated with the pro- 

 ducts of decomposition of the tissues, which have transuded into the inter- 

 stices of organs from the capillaries. It likewise takes up, during the 

 period of digestion, by means of its radials terminating in the mucous 

 membrane of the small intestine, that fluid known as chyle, which has 

 been already referred to (p. 131). Owing to the fact, therefore, that the 

 lymphatic system is only destined for the conveyance of these matters 

 into the circulation, it is entirely wanting in vessels corresponding to the 

 arteries. It consists rather of a set of vessels corresponding to the 

 capillary part of the circulation, and of drainage tubes taking their rise 

 from those which may be compared to the veins. 



Lymphatic vessels are widely distributed throughout the body, but 

 occur most abundantly in vascular parts. They have, however, been 

 missed, up to the present in certain portions of the body well supplied with 

 blood. They are not found in such non-vascular tissues as the epidermis, 

 nails, and cartilages. 



The mode of origin of lymphatics was for a long time veiled in the 

 deepest obscurity, owing to the fact that the numerous valves of the 

 larger trunks offered the most determined resistance to injection, and thai 

 the colourless nature of the contents of the finer tubes rendered their 

 immediate recognition almost impossible. Further, it is only certain 

 specially transparent parts that allow of the latter being seen at all. That 



