72 NORMAL HISTOLOGY. 



or fibrous tissue. This subsequently " ossifies/' during which pro- 

 cess it is not really converted into bone, but is gradually absorbed 

 as that tissue develops and replaces it. 



III. THE FIBROUS TISSUES. 



General Characters. This group of elementary tissues, which 

 may be said to constitute the connective tissues par excellence, 

 includes a number of varieties which are not very sharply defined, 

 because of transitional modifications which bridge over the differ- 

 ences between the more distinct types. It will, therefore, be best 

 to describe these well-marked types of structure, and then to indi- 

 cate the direction in which they are modified in particular cases so 

 as to simulate in greater or less degree other typical varieties of the 

 same group. 



(1) The cells of the fibrous tissues vary considerably in character, 

 three more or less distinct forms being distinguishable. First, flat- 

 tened, almost membranous cells with oval nuclei and nearly clear 

 and homogeneous bodies, possibly identical with the cells that form 

 endothelium ; second, granular cells, rich in cytoplasm and usually 

 ovoid or cubical shape, though sometimes elongated ; third, elon- 

 gated or fusiform cells, with oval nuclei surrounded by a moderate 

 amount of cytoplasm which is frequently prolonged into processes 

 of greater or less length and delicacy, and sometimes dividing into 

 branches. These three sorts of cell are present in varying relative 

 proportions in the different tissues belonging to this group. (2) 

 The intercellular substance is composed of distinct fibres, asso- 

 ciated with a homogeneous cement- or " ground-substance," lying 

 between the fibres. The fibres are of two kinds : the " white," 

 non-elastic, and the elastic or " yellow." The relative abundance 

 of these and of the ground-substance associated with them, and 

 also their arrangement, vary greatly in the different members of 

 the group. (3) The arrangement of the constituents of the fibrous 

 tissues in the different varieties is so diverse that a statement of the 

 variations would amount to a description of the tissues themselves. 

 The general characters already enumerated will serve to distinguish 

 the whole group from all the other elementary tissues, and enable 

 the student to recognize the fact that a given form of the tissue 

 which he may have under observation belongs to this group. 



Before entering upon a description of the varieties of fibrous 



