TISSUES. 65 



ference in the degree of condensation of the inter- 

 cellular substance, being either loosely arranged as 

 in reticular connective tissue, or more compact as in 

 tendons, or a greater degree of condensation as in 

 cartilage, bone, and dentine. In all these types the 

 cellular elements are morphologically very similar, 

 which makes it possible for one form to develop into 

 that of another; for instance, bone is produced from 

 cartilage, or from fibrous connective tissues. 



The function of supporting tissue is largely a pas- 

 sive one depending on its physical properties, and the 

 amount of nourishment the cellular elements re- 

 ceive is therefore a very variable quantity. Ten- 

 dons, particularly, have a limited supply, perhaps 

 because the cells form so small a part of these struc- 

 tures. Nutrition is supplied from the lymph which 

 penetrates the ground substance through clefts or 

 minute channels placed in the intercellular material 

 of the more condensed forms. In bone fine canals 

 develop and anastomose to form a canalicular sys- 

 tem, while in other forms, as mucous connective tis- 

 sue and hyaline cartilage, the nourishing lymph 

 seems to pass through the ground substance regard- 

 less of lymph channels, as in these cases the latter 

 have not been found. 



Blood vessels and capillaries ramify more or less 

 freely through the matrix of supporting tissue, ex- 

 cept in case of cartilage, where they are practically 

 absent. Unlike epithelia, nerves may be abundant, 

 but in no case do nerve fibers unite with the cellu- 

 lar elements ; however, special sensory nerve endings 



5 



