EXCAVATION OF THE CARTILAGINOUS OTIC CAPSULE 



' • m4S^ ^vM^^jf otic vesicle 



^mmMm-f 



► Capsule 



C^' 



Ad) ac e nt 



m es en c hyme 



•"CS) 



Fig. 3 Camera lucida drawing of a portion of the otic capsule while it is the 

 state of condensed mesenchyme. It is taken from a human embryo 13.5 mm. 

 long (Carnegie Collection, No. 695). The section is 10 microns thick and is 

 enlarged 950 diameters. The syncytial character of the capsule can be seen 

 and also its relation to the epithelial wall of the otic vesicle and to the surround- 

 ing mesenchyme. 



STAGE OF PRECARTILAGE 



The histogenetic changes which initiate the conversion of the 

 capsule of condensed mesenchyme into a cartilage-hke tissue 

 make their first appearance just after the separation of the 

 semicircular ducts from the main vestibular pouch. This occurs 

 when the embryo is about 14 mm. long. The conversion of the 



