124 ELASTIC TISSUE. 



unless the tissue is investigated in a very young foetus, we can 

 only detect cell-nuclei intermixed with fibres, or nuclei, in 

 whose immediate proximity a small fasciculus of fibres arises 

 on both sides. At an early stage of development the tendons 

 have a gray appearance, not having assumed the white colour 

 of the adult tissue. This fact is probably connected with 

 a chemical difference existing between the young and perfectly 

 developed fibrous tissue, as in areolar tissue. The quantity of 

 the cytoblastema in which these cells are formed, and by which 

 the fibres and tendons, when perfected, are probably connected 

 together, must be extremely small, and cannot in any way be 

 demonstrated by observation. Its existence can only be inferred 

 by analogy with areolar tissue : it will be remembered that it 

 was proved to be present in the foetal condition of that tissue. 

 The quantity of cytoblastema, in comparison to the fibres pre- 

 sent, seems to me to be the principal distinction between areolar 

 and fibrous tissue in the adult. The fibrous tissue contains 

 a great many more fibres within a given space than the areolar 

 does, and they are not more minute than those of the latter 

 tissue. There is just as great a difference, however, between 

 fibres of areolar tissue tali en from different parts of the body, 

 as there is between the ordinary fibres of tendons and the most 

 common form of areolar tissue, so that a very gradual transi- 

 tion takes place. 



3. Elastic Tissue. The distinction between elastic and 

 fibrous tissue is exhibited at a very early period. But my 

 investigations into the history of the development of this tissue 

 are very incomplete, and extended only so far as to render 

 it probable that it presented no exception to the principle of 

 development from cells. I made use of the aorta of a foetal 

 pig and the ligamentum nuchse of a foetal sheep for the purpose. 

 The tissue taken from these two parts was very, different in its 

 general character. In a pig's embryo, of six inches in length, 

 the aorta had already acquired its yellowish colour and perfect 

 elasticity. The external coat could be easily drawn off in 

 long pieces, almost, indeed, as a distinct tube. Having drawn 

 off a small portion of the middle coat (which, in order to avoid 

 any suspicion of epithelium being mixed w T ith it, was so care- 

 fully done, that the internal surface of the vessel remained 



