ORGANS OF THE BODY. 



407 



muscular tissue ( 170, p. 295). The occurrence in it alone of inosite is 

 a fact of great interest. 



The structure of the arteries and veins has been already discussed in 

 203 and 204, that of the capillaries in 201 and 202. 



222. 



We now turn to the consideration of those peculiar bean-shaped and 

 very vascular organs, the lymphatic glands or lymph-nudes, which occur 

 in the bodies of the higher vertebrates, interrupting the course of the 

 larger absorbent vessels. They are met with in greatest number on the 

 lymphatic trunks of the intestines, and at those points where superficial 

 and deeper sets of vessels join. It not unfrequently comes to pass that 

 one single vessel is in this way interrupted over and over again by sucli 

 nodes, and it is probable that every trunk in its course from the peri- 

 phery to the ductus thoracicus has at least one such. In those lymph- 

 nodes, which are not very minute (fig. 380, a), we usually find several 

 lymphatic twigs penetrating into their interior from the convex border. 

 These are the vasa afferentia (/, /). From the other side either one or 

 more vessels (in the first case of greater calibre), make their exit, known 

 as the vasa efferent ia (h). This takes place as a rule at a point where a kind 

 of depression may be observed, and where the larger blood-vessels enter 

 the organ. This spot, when the depression is present, is named the bilus 

 (h). It is entirely absent, however, in many glands. 



The internal arrangement of the lymph-nodes is a point most difficult 

 to determine, and it is only very recently that any satisfactory insight has 

 been gained into their 

 minute structure. We 

 learn, besides, from recent 

 observations, that the organs 

 in. question display consi- 

 derable variety, both as re- 

 gards volume, compared 

 with the size of the mam- 

 mal body, and also their 

 locality ; so that the struc- 

 ture, for instance, of a 

 large lymph-node from an 

 ox, and a small one from 

 a rabbit or Guinea-pig, 

 exhibits great difference. 

 Were this axiom allowed 

 its due weight, we should 

 be spared many unprofit- 

 able controversies. 



In those lymph -nodes 

 which are riot altogether too small we can distinguish a reddish grey cor- 

 tical portion, consisting of round bodies, the follicles (d), and a darker 

 spongy medullary portion, composed of the tubes and reticular prolonga- 

 tions (e) of these follicles. 



Each lymphatic gland is enclosed in a thicker or thinner fibrous enve- 

 lope (a), moderately vascular, and consisting of ordinary connective-tissue 

 cells, fibrillated interstitial substance, and elastic elements. A continuous 

 layer of muscular tissue does not occur in this envelope. The outer 

 27 



Fig. 398. Section of a small lymphatic gland, half diagram- 

 matically given, with the course of the lymph, a, the enve- 

 lope ; 6, septa between the follicles or alveoli of the cortical 

 portion; c, system of septa of the medullary portion, down 

 to the bilus of the organ; e, lymph-tubes of the medullary 

 mass; /, different lymphatic streams which surround the 

 follicles, and flow through the interstices of the medullary 

 portion ; gr, confluence ot these passing through the efferent 

 vessel; 7i, at the bilus of the organ. 



