70 CONNECTIVE TISSUE. 



3. A third variety of connective tissue is commonly met ^vith in 

 the form of delicate membranes and was formerly supposed to be 

 quite homogeneous in structure. These membranes have, however, 

 in almost every case, been shown to be made up of flattened cells, in 

 close apposition, and more or less fused together by their edges, which 

 can, however, be brought to view by staining with nitrate of silver. 

 Examples of such are to be found in the walls of the capillaries, the 

 hyaloid membrane of the eye and the membrame propruc lying under 

 the epithelium of mucous membranes at certain parts, in gland ducts 

 and the like. 



It must be noted, however, that some homogeneous membranes, as 

 for example, the posterior elastic lamina of the cornea, are of a different 

 nature. 



DEVELOPMENT OF THE CONNECTIVE TISSUE. 



Those parts of the early embryo in which connective tissue is subse- 

 quently to be developed, are at first composed entirely of closely 

 agglomerated embryonic cells, to all appearance similar to those of 

 which the remainder of the body is constituted (see p. 8). The first 

 change of importance that occurs is the development of blood-vessels 

 from some of these cells in the manner that has already been partly 

 explained (p. 41), and will be further treated of when those vessels 

 have come under consideration. Soon after the development of these 

 primitive blood-vessels the embryonic cells become more separated, but 

 retain for the most part a connection with one another by interjoining 

 processes ; and the interstices between the cells are now found to be 

 filled with a clear fluid, as to Avhich it is uncertain Avhether it is pro- 

 duced by the cells themselves, or derived directly by transudation from 

 the blood-vessels, as Boll is inclined to believe : it is to be noted, how- 

 ever, that besides albumin this fluid contains mucin, which is commonly a 

 product of cells and is not demonstrable in the liquor sanguinis. This 

 muco-albuminous fluid subsequently acquires a firmer consistence and 

 eventually remains as the ground substance, which in the adult 

 tissue, although widely diffused, is nevertheless, relatively to the fibres, 

 in very small amount. A difference is noticeable in the relations 

 of the cells according as areolar or fibrous tissue is to become 

 developed, they being in the former case connected together both 

 laterally and at their ends, in the latter at their ends merely ; rows 

 or chains of cells being thus produced. Before long a delicate 

 striation appears within the cells, in the case of the fibrous tissues in a 

 longitudinal direction only, in that of the areolar obliquely and 

 transversely as well : this striation (which afterwards passes into 

 fibrillation) may be traced through the connecting processes from 

 one cell into another. In this manner each bundle of fibrils is 

 produced from a series of connected cells by the conversion of 

 the whole or of a part only of their protoplasm into coilogenous sub- 

 stance : in the latter case the remainder of the cell becomes flattened 

 out and persists on the surface of the bundle as a connective-tissue 

 corpuscle or tendon-cell, as the case may be. In the areolar tissue 

 many of the smaller bundles or threads are formed from processes 

 wdiich grow out from the corpuscles into the suiTounding ground-sub- 

 stance, and, interlacing and intertwining with processes from other cells. 



