CONTAINED PERIOTIC TISSUE-SPACES IN THE HUMAN EMBRYO. 37 



In many instances capsules are found containing more than one cartilage cell, 

 showing the tendency to cell columns. 



A casual glance at a section under lower powers might indicate that the inner 

 margin of the cartilage is in direct contact with the perichondrium. Examination 

 under higher magnification, however, shows that between the thick perichondrium 

 and the cartilage there is a narrow zone of dedifferentiated cartilage. In it the 

 matrix has largely disappeared and the capsules have collapsed and are flattened 

 out, allowing the elongated endoplasm of adjacent cartilage cells to come in con- 

 tact, separated only by the remnants of the capsular margins. Dyes that stain 

 endoplasm red cause this zone to appear as a deep-red line. This zone represents 

 a state of transition between cartilage and precartilage and its presence doubtless 

 indicates that the margin of the cartilage is still in an unstable condition. The 

 narrowness of the zone and the abruptness of the transition are characteristic of 

 later stages, where the process is more gradual and relatively small in amount. 

 The transition from this zone to the perichondrium is likewise abrupt. The peri- 

 chondrium consists of a dense protoplasmic stratum thickly studded with nuclei, 

 and has all the appearance of late embryonic fibrous connective tissue. It is of 

 about the same thickness around the whole margin of the canal. At the outer 

 margin (toward the right) it fuses with the membrana propria of the epithelial 

 duct, thereby forming an attachment which is regarded as a suspensory ligament 

 for the support of the membranous labyrinth. The trabeculse of the reticulum 

 extending between the membrana propria and the perichondrium are just begin- 

 ning to break apart, allowing the adjacent spaces of the reticulum, as they are seen 

 in section, to coalesce in the formation of larger spaces. 



Having completed the review of the early history of the reticulum and its 

 formative relations to the adjacent tissues, we are now in a position to consider 

 the development and the fate of these larger spaces in the reticulum, which have 

 hitherto been generally known by the misleading term "perilymphatic spaces." 



DEVELOPMENT OF PERIOTIC TISSUE SPACES. 



In the preceding pages of this article the main features of the development of 

 the cartilaginous capsule that incloses the membranous labyrinth have been 

 described. We have traced the process step by step from the first condensation 

 of the mesenchyme around the otic vesicle, through its differentiation into a pre- 

 cartilaginous mass and the maturation of the latter into true cartilage, with the 

 formation through dedifferentiation of cartilaginous chambers in which the mem- 

 branous labyrinth is suspended. It has been shown how these spaces within the 

 cartilaginous capsule are modified in adaptation to the continued growth of the 

 membranous labyrinth and how they finally come to be filled with an open-meshed 

 reticulum which everywhere bridges the space existing between the membranous 

 labyrinth and the surrounding cartilage. It has further been shown that the mem- 

 brana propria supporting the epithelial part of the labyrinth on the one hand and 

 the perichondrium on the other are derived from and serve as the limiting mem- 

 branes of this reticulum. It is a modification in the meshes of this same reticulum 



