Homografts of the middle ear. Privileged tissue or privileged site

To explain the survival and behavior of homografts, we have tried, by means of discussion and use of biological models, to resolve a problem with three unknowns, ie, the tympanic membrane, the ossicle, and the middle ear, with the notions of privileged tissue and privileged site. The tympanic membrane survives because of the relative stability of its fibers and the absence of mechanical trauma. Later, the membrane is sheathed by fibrous tissue. The ossicle is not only tolerated by the host but is also invaded and ossified.