4 2 CONNECTIVE TISSUES. [sect. 22. 



forms which present an important difference from the other two, 

 and seem to render a metamorphosis into them impossible. As 

 already remarked, these three tissues do not represent so many 

 evolutional forms belonging to one and the same series, but rather, 

 as it were, parallel conditions manifesting themselves throughout a 

 larger group of tissues. Instances of such peculiar forms are af- 

 forded by the mucous tissue when its cells have vanished, reticular 

 cartilage, and elastic tissue, in which last the gelatiniferous or white 

 fibrous tissue is reduced to insignificance, and the specially trans- 

 formed corpuscles come to predominate. 



A more important proof of the intimate connection of the three 

 tissues m question is, that, firstly, all are capable of passing into 

 osseous tissue; and, secondly, they are very frequently substituted, 

 the one for the other, in the animal series. With regard to the 

 former point, the recent investigations, since those of Sharpey and 

 myself, have shown with certainty that not only cartilage, but 

 even connective tissue, may be converted into true bone, in which 

 case its fibrous substance becomes ossified, and the corpuscles are 

 transformed into bone-cells. Mucous tissue likewise appears, at 

 least in abnormal conditions, capable of conversion into bone, as 

 seen m ossifications occurring in the vitreous humour; so that' all 

 the three members of the first series of connective substance, how- 

 ever different they may be, may all lead to a similar result. All 

 forms of connective substances can, likewise, mutually take the 

 place of each other in one and the same organ, as is more especially 

 observable in the skeleton, which appears in almost every modifi- 

 cation of connective tissue, cartilage, and bone; further, in the 

 skm, which not only repeats the different forms of mucous and 

 connective tissues, but also presents osseous, and cartilaginous, and 

 even dental formations of the most diverse kinds. 



If, after this general consideration, we cast a glance at the indi- 

 vidual parts which enter into the composition of connective sub- 

 stances, we observe the following :— The matrix, occurring in all 

 of them, presents, in its development, two essentially different 

 types. In connective tissue it is chiefly formed by a coalescence of 

 elongated (perhaps, also, round) cells, whilst in mucous and carti- 

 laginous tissue it is more especially intercellular substance. Yet 

 even m connective tissue, there is formed, in certain cases (in ge- 

 latinoid connective tissue), along with the matrix proceeding from 

 cells, a distinct intercellular substance; while, on the other hand 

 in cartilages, the external secondary membranes of the cartila-e- 

 cells participate in the formation of the intermediate substance 



