EXCAVATION OF THE CARTILAGINOUS OTIC CAPSULE 19 



rower and more sharply outlined, as is common in older fetuses, 

 the alteration is then proceeding more slowly. 



The dedifferentiation of cartilage into precartilage involves 

 first of all changes in its matrix including the loss of its tinctorial 

 reaction, a decrease in its amount and an alteration in its struc- 

 tural appearance, in that it becomes less homogeneous and begins 

 to show the presence of branching processes. As a result of 

 these changes in the matrix, the encapsulated cartilage cells 

 come to lie closer together, pressing to some extent directly 

 against each other. The combined edges of the overlapping 

 margins of flattened capsules give the appearance of wavy re- 

 fractile lines running through the transition zone parallel to the 

 margin of the canal. With these changes the capsules of the 

 cartilage cells rapidly become incomplete and take on the appear- 

 ance of branching processes. With the disappearance of the 

 capsules the tissue assumes the appearance of a mesenchymal 

 syncytium which then takes on a reticular character and becomes 

 part of the general periotic reticulum. The question as to whether 

 there is an active proliferation of the nuclei in the tissues 

 subsequent to their alteration from cartilage to precartilage has 

 not been definitely detennined. The material at hand is in- 

 adequate for a satisfactory solution of this point, although in 

 some specimens there seems to be an increase in the number of 

 nuclei in the transition zones of precartilage, over and above 

 the apparent increase associated with the absorption of the inter- 

 vening matrix, which could only be explained in that way. It 

 would seem very probable that with its dedifferentiation there 

 should be associated a renewed proliferative vitality of a given 

 embjTonic tissue, sufficient at least for its reconstruction into 

 the newer form. 



DEVELOPMENT OF THE PERICHONDRIUM 



In studying the cartilaginous canals one must take into con- 

 sideration the perichondrium and its relation to the continual 

 transformations occurring along their margins. Reasoning from 

 the prevaihng conceptions, concerning the activity of periosteum 

 in bone growth, one might expect to find in the perichondrium 



