THE HISTOGENESIS AND GROWTH OF THE OTIC CAPSULE AND ITS 

 CONTAINED PERIOTIC TISSUE-SPACES IN THE HUMAN EMBRYO. 



BY GEORGE L. STREETER 



INTRODUCTION. 



During the past year the writer has published two shorter communications 

 regarding the development of the connective tissue and cartilaginous coverings that 

 inclose the membranous labyrinth, one of which dealt with the histogenesis of the 

 cartilaginous capsule and the other with the periotic tissue-spaces that are formed in 

 the interval between the cartilaginous capsule and the membranous labyrinth. In 

 the present paper the same matter will be treated in more complete form and a 

 general description will be given of the development of the otic capsule as a whole 

 and of the problems involved in its growth. 



In making this study the effort has not been so much toward the determination 

 of the exact form of the capsule as it has been toward the detection of some of the 

 factors that are involved in the production of this form. These two problems, 

 however, are not to be altogether separated. It is the distinctive form of the otic 

 capsule that makes it a particularly favorable place for determining the histological 

 features of the growth of such a structure. Owing to the fact that it is so well 

 provided with known landmarks, the changes in its size and form can be accurately 

 followed and it is therefore possible to determine deductively at what points, for 

 instance, new cartilage is being laid down and at what points it is being removed. 



It was soon recognized that the growth of the otic capsule resolves itself into an 

 increase in its external dimensions and a simultaneous hollowing-out and reshaping 

 of its contained cavities, the latter being so managed that their general form and 

 proportions are continuously maintained and a suitable space always provided for 

 the enlarging membranous labyrinth. It is particularly the feature of cartilage 

 excavation accompanying the increase in the total mass to which attention will be 

 invited. It is quite evident that such growth can not be explained on the basis of 

 a simple interstitial increase in the amount of cartilage, together with its passive 

 rearrangement to allow for the enlarging cavities, due, one might say, to a mechanical 

 expansive pressure from the growing membranous labyrinth with its surrounding 

 tissue and fluid. Such a passive rearrangement could only occur in a tissue that is 

 very plastic, whereas cartilage is one of the least plastic of the embryonic tissues. 

 Moreover, the histological picture is not that of mechanical pressure; the cartilagi- 

 nous chambers are always excavated slightly in advance of the space actually 

 required by the membranous labyrinth, and there is no evidence of the labyrinth 

 being cramped or of the creation of pressure grooves in the margin of the cartilage. 



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