468 RETICULAR TISSUE. [BOOK n. 



the rest of the mucous membrane above, the muscle itself being 

 also well provided with blood vessels. 



The connective tissue which occupies the whole of the narrow 

 irregular zone between the basement membrane above and the 

 muscularis mucosae below, except for the space taken up by the 

 blood vessels and definite lymphatic vessels (of which we shall 

 presently speak), is of a kind which, though it is not quite the 

 same in the villi as elsewhere, is on the whole closely allied to 

 the kind known under the various names of retiform or reticular 

 connective tissue, adenoid tissue or lymphoid tissue, and indeed is 

 often called by one or other of these names. 



Typical adenoid tissue such as is met with in the lymphatic 

 follicles of the intestine, of which we shall presently have to speak, 

 in lymphatic glands and elsewhere, presents the appearance of a 

 fine close-set and fairly regular network with meshes so small as 

 not to afford room for more than one or two leucocytes in each 

 mesh. The bars of the network are delicate fibres composed of 

 material which is similar to, if not identical with, that of the 

 fibrillae of ordinary connective tissue. At the nodal points of 

 the network thickenings are frequently but not always present, 

 and some of the more conspicuous of these thickenings may 

 contain nuclei either spherical in form or more or less misshapen ; 

 but such nuclei are not numerous. Adenoid tissue in fact is 

 composed of anastomosing branched cells, the greater part of the 

 cell in most cases, and indeed the whole of the cell in some cases, 

 having been transformed into filamentous processes, of a differen- 

 tiated nature, which join freely with each other and with the 

 like processes of other cells to form a fine regular network, a 

 portion only of the cell, sometimes with and sometimes without 

 its nucleus (this having disappeared), being left to form a nodal 

 thickening. 



It may be regarded as a less developed form of connective 

 tissue than the white fibrous or the ordinary areolar connective 

 tissue. In the earlier stage of its development in the embryo 

 connective tissue of all kinds is represented by a number of nu- 

 cleated granular protoplasmic cells, lying in a fluid or nearly fluid 

 matrix. The cell-bodies are branched, the branches joining together 

 at intervals to form a network. In the development of ordinary 

 connective tissue the outer portion of the cell-body of some of the 

 cells is converted into or at least gives rise to fibrillar gelatinife- 

 rous material, or the whole of it may be so converted, the rest of 

 the cell, or other cells, being left as connective-tissue corpuscles. 

 In adenoid tissue the cells remain as branched cells, joining into 

 a network, and the cell-substance is not in any part transformed 

 into bundles of fibrillae, though it has undergone, besides an 

 increase in its branching, in part at all events, a chemical trans- 

 formation, since the material forming the bars of the network is in 

 a large measure no longer ordinary ' protoplasmic ' cell-substance. 



