4 GEORGE L. STREETER 



explanation of the deposit of new cartilage or of the excavation 

 of the old, since the perichondrium, as will be shown, does not 

 make its appearance until after a considerable amount of the 

 growth and hollowing-out of the labyrinth had been already 

 completed. Therefore there is involved in the development of 

 the cartilaginous capsule something more than interstitial and 

 perichondrial growth, in the ordinary sense of the terms. On 

 account of its bearing upon this problem, it is the purpose of 

 the present paper to call attention to the occurrence of dedif- 

 ferentiation of cartilage in the human embryo, and to point out 

 the important part which this process normally plays in the 

 hollowing out and reshaping of the otic capsule during its 

 development. 



The term dedifTerentiation is applied here in the sense of a 

 regression of certain areas of cartilaginous tissue to a more 

 embryonic form, the same areas being subsequently rebuilt or 

 redifferentiated into quite a different type of tissue. Dedif- 

 ferentiation is defined by Child as ''a process of loss of differ- 

 entiation, of apparent simplification, of return or approach to 

 the embryonic or undifferentiated condition." In his note- 

 worthy review of this subject he makes the assertion that the 

 wide occurrence and significance of dedifTerentiation in the 

 lower animals and plants "must at least raise the question 

 whether similar processes do not occur to some extent in higher 

 forms. "2 From the context it is evident that he refers to man 

 as well as other mammals. The materialization of his predic- 

 tion is here at hand in the development of the cartilaginous 

 capsule of the ear. Before entering into this further it will be 

 necessary to outline the earlier steps in the histogenesis of this 

 particular tissue. 



THE THREE STAGES IN THE DEVELOPMENT OF CARTILAGE 



The cartilage of the otic capsule in its transition from 

 embryonic mesenchyme to true cartilage passes through three 

 fairly definite phases: firstly, the condensation of mesenchyme 



^^hild, C. M. Senescence and rejuvenescence. University of Chicago 

 Press, 1915. Page 293. 



