ORGANS OF THE BODY. 



491 



Fig. 484, From the surface of the pro- 

 cessus vermiformis of the rabbit, a, 

 narrowed entry to the cupola of a fol- 

 licle ; 6, mouths of crypts in the broad 

 ridge of mucous membrane; c, hori- 

 zontal lymphatic network ; d, descend- 

 ing lymph canals. 



the follicles of one gland by means of a tissue entirely iRmilar to their 

 own. It is also continuous, without any line of demarcation, with the 

 adjacent infiltrated retiform tissue. It is at its level that we usually find 

 the muscularis mucosce (c) which opens in each case to allow room for 

 the follicles (Frey). 



We must now turn to the nearer consideration of the cupolse. These 

 are surrounded by annular ridges of mu- 

 cous membrane, containing follicles of Lie- 

 berkuhn (b), and are continuous down- 

 wards into the mesial zones, supporting on 

 their free surface, either ordinary or, what 

 is more frequently the case, somewhat 

 modified irregular villi (a). The actual 

 summits of the follicles, however, are quite 

 destitute of villi. They are, in fact, so 

 freely exposed that each lymph follicle 

 appears to the naked eye as a little pit 

 on the surface of the plaque. 



The ridges around the follicles may, 

 however, as in the plaques of the colon, 

 be quite bare of villi. In the processes 

 vermiformis of the rabbit, also, the surfaces of the rings may be increased 

 greatly in breadth (fig. 484, 5), so that only a narrow entrance (a) to the 

 follicles is left. 



If we turn now to the finer structure of the elements of Peyer's patches, 

 we find it to be exactly 

 that of other lymphoid 

 follicles. Their sustenta- 

 cular tissue is a species of 

 retiform connective sub- 

 stance, traversed by capil- 

 laries in which innumer- 

 able lymph cells are 

 entangled (pp. 195 and 

 420). Many of the nodal 

 points in this network 

 contain in young indivi- 

 duals full-bodied nuclei, 

 met with in adults, on the 

 other hand, in a shrunken 

 condition. At the mesial 

 zone this reticular tissue 

 is continuous with the similarly constituted connecting lymphoid layer, 

 and through this with the closely related tissue of the mucous membrane. 



The sustentacular matter in the interior of the follicles is very loosely 

 interwoven, while externally it assumes a denser texture. 



At two spots it becomes exceedingly densely reticulated and distinct ; 

 in the first place on the surface of the cupola, which is, like the villi, 

 covered immediately by columnar epithelium, and then at the peripheral 

 portion of the base. This latter in some of Peyer's glands is surrounded 

 by a continuous investing space, which corresponds to the investing 

 spaces of the lymphatic glands ( 223). In many animals the resem- 

 blance is increased by the interposition o/ perpendicular fibrous septa 



Pig. 485. Vertical section through an injected Payer's follicle 

 of the rabbit, showing the capillary network of the same; the 

 large lateral vessels, 6, and those of the villi, c. 



