TISSUES, ORGANS, AND SYSTEMS. 7 7 



few or wanting. The adipose tissue occurs principally in the 

 skin, forming the panniculus adiposus ; in the larger cylindrical 

 bones, as yellow bone-medulla ; in the orbit ; around the 

 kidneys ; in the mesentery and the omentum ; around the spinal 

 marrow; in nerves and vessels, and in muscles. The areolated 

 connective tissue is widely distributed between the separate 

 organs and viscera of the neck, thorax, abdomen, and pelvis, 

 and everywhere along the course of the vessels and nerves, 

 and in the interior of the muscles, nerves, and glands. 



[The connective tissue is found in all the four classes of the 

 vertebrata, in about the same condition as in man ; while, on 

 the other hand, in the invertebrata it is very rare, and when 

 present is more homogeneous, or consists of isolated cells and 

 intermediate substance, rarely more fibrous, as in Cephalopoda, 

 in the mantle of bivalves, in the peduncle of the Linguke, and 

 of the Cirripeds. Fat-cells also do not occur among the lower 

 animals to the same extent as among the higher. The firm 

 connective tissue is here replaced by a chitinous substance, or 

 by one consisting of cellulose, and by calcareous or horny tissues. 



Opinions are still divided as to the structure and develop- 

 ment of the connective tissue. Whilst the majority ascribe a 

 distinctly fibrous structure to it, and suppose it to consist of 

 bundles, and these again of fibrils, Reichert considers this 

 tissue to be more homogeneous, and regards the fibrillation 

 partly as artificial, partly as the expression of a folding, a view 

 to which Bidder and Yirchow are also inclined. For my own 

 part, I find a certain amount of truth in Reichert' s conception, 

 insomuch as it is not to be denied that there also exists a non- 

 fibrillated, more homogeneous connective tissue, which had 

 previously been little investigated ; but I am nevertheless of 

 opinion, that, as applied to the great mass of the organs com- 

 posed of connective tissue, it is incorrect. The possibility of 

 making out fibrils in delicate membranes, even without pre- 

 paration, the ease with which these may be isolated in tendons 

 and ligaments, and lastly, the circumstance that the fibrils may 

 be demonstrated upon transverse sections of the tendons, and 

 of the more solid connective tissue in general, are for me suffi- 

 cient reasons for retaining the old view. 



With respect to the development of the connective tissue, I 



