ORGANS OF THE BODY. 



421 



have seen it in the lymph-nodes ( 223). The vascularity of these mucous 

 follicles is liable to vary to a considerable extent. In some of them, such 

 as those of the conjunctiva, 

 the capillaries only occur 

 sparsely, in the form of 

 very open interlacements ; 

 while in other cases we ob- 

 serve an extremely com- 

 plex and delicate network, 

 the tubes having, to a cer- 

 tain extent, a radiating 

 arrangement when viewed 

 in transverse section. Fig. 

 412, sketched from such 

 a preparation of one of 

 Payer's patches from the 

 rabbit, will serve as an 

 example of the latter form. 

 These rounded follicles, 

 sometimes spherical and at 

 others vertically elongated, 

 are situated either in the 

 tissue of the mucous mem- 

 brane itself, or when of 

 considerable length, they 

 project down into the sub 



mucosa. Their upper por- 



Fip. 413. Transverse section through the equator of three 

 Payer's patches of the same animal, a, the capillary net- 

 work ; 6, of the larger circular vessels. 



tion [the cupola (fig. 414, d)] may be covered by a thin layer of mucous 

 tissue [conjunctival follicle (fig. 415)], but may also advance so far for- 

 wards as to be covered merely by an epithelial coating lying directly 

 on the reticulated sustentacular tissue [tonsil Peyer's follicles (fig. 

 413)]. 



In the middle equatorial region [" mesial or equatorial zone" (fig. 414, e)] 

 the follicle is connected to a greater or less extent with the adjacent parts ; 

 sometimes with the neighbouring mucous tissue, which in that case pre- 

 sents, for a certain distance, the same reticular character, containing also 

 lymph corpuscles, and at other points with abutting follicles. Thus we 

 see, for instance, in the vermiform appendix of the rabbit a portion of 

 the intestine consisting entirely of crowded oval follicles that the latter 

 are regularly united in the neighbourhood of their equator by bands of 

 lymphoid tissue (fig. 412), whilst the whole lower half of the follicle (the 

 base) exhibits the same continuous investing space as in the lymph nodes. 

 The analogy, however, is even more perfect than might be inferred at 

 first sight, for careful observation teaches that here also a system of 

 fibrous septa exists, which, springing from the submucosa, passes under 

 the follicles, and sends up partitions perpendicularly between them. 

 These spaces are even lined by the same characteristic endothelial cells, 

 as those seen in the lymph nodes, according to His. 



Should these extensive investing spaces be absent, the follicles of each 

 group are usually united to one another by means of reticular lymphoid 

 tissue. The latter, in contradistinction to that of which the follicle itself 

 is composed, exhibits a much closer texture, so that under the microscope 

 it appears as a dense and non-transparent layer, within which the more 



