[Chondroid tissue].

Nearly impossible to evidence with classical paraffin sections, chondroid tissue is regularly absent in the chapters of textbooks dealing with skeletal growth in which however it represents one of the major constituents. Microradiograph and methylene blue surface staining of thick undecalcified sections are the most suitable methods to reveal the presence of chondroid tissue. Moreover, all the methods used clearly indicate that this tissue is different from both calcified cartilage and woven bone or lamellar bone. The simultaneous presence, within the chondroid tissue matrix, of collagen type I, specific for bone tissue, and type II, specific for cartilage enables also to distinguish chondroid tissue from all the other calcified tissues. The presence of chondroid tissue in both fetal mandibular symphysis and in the sutural spaces of the skull strongly suggests that the same biomechanical stresses have the same consequences, i.e. the growth of the tongue separates the hemimandibles and the development of the brain has the same effect on the sutural areas. Experimental production of chondroid tissue is obtained in the space appeared between the bone fragments submitted to a continuous distraction. Finally, since the first cranial vault is also constituted by chondroid tissue islets, it has to be concluded that bone tissue is always secondary in its origin, i.e., after hyaline cartilage in endochondral ossification and after chondroid tissue in membranous ossification.