DEVELOPMENT OF CELLULAR TISSUE. 335 



According to my observations, both forms of cellular 

 tissue originate in cells. 



The cells of the white fibrous tissue exist first as rounded 

 nuclei, around which the cell wall gradually makes its appear- 

 ance, and these cells when fully formed are large, granular, 

 elongated, fusiform, and from each extremity at length pro- 

 ceeds a single unbranched thread, which gradually becomes 

 extended into a filament or fibre, which is produced by the 

 growth and extension of the cell wall itself, and the extremity 

 of which unites for the production of an elongated thread 

 with that proceeding from the other cells placed above and 

 below it : finally, the process terminates by the absorption 

 of the nuclei. (See Plate XLIII. Jig. 2.) 



The cells of the yellow fibrous tissue also exist, at first as 

 nuclei, then as fusiform cells, but differ from those of the 

 white fibrous tissue in the subsequent steps of their develop- 

 ment, in that the cells are disposed in lines, each fibre being 

 formed, as is the case with the unstriped muscular fibre, by 

 the union of the filaments, proceeding from each series of 

 linearly disposed cells, and in that the filaments proceeding 

 from the cells are very frequently branched. (See Plate 

 XXXIX. figs. 1, 2. Plate XL. figs. 3. 5.) 



The above described mode of development may be fol- 

 lowed out in longitudinal and cross sections of tendon treated 

 with acetic acid, also in the smaller vessels of the pia mater, 

 and in those placed in the mixed cellular tissue which sepa- 

 rates ' the different striped muscular fasciculi : we thus per- 

 ceive, that in the case of the yellow fibrous tissue, many 

 nuclei are required to form a single filament ; and further, 

 that there is a strong analogy in the mode of its develop- 

 ment with that of muscular fibre, as also in the physical pro- 

 perties of the two tissues. 



In the fibrillation of the fibrin of the blood we have an 

 example of the formation of filaments independently of any 

 development from cells, and at one time I conceived that the 

 fibres 'of the white fibrous tissue might possibly originate in 

 a similar manner. 



