EXCAVATION OF THE CARTILAGINOUS OTIC CAPSULE 



21 



lial margin. The reUition of the perichondriuiu to the reticular 

 tissue surrounding the labyrinth, as seen under higher mag- 

 nification, is shown in figure 12. The section is a portion of 

 the one shown in figure 11 and includes the successive strata 



Ductus semicirc. post. 



•^Cartilac^e 



-Precartilaqe 



X'X 



: .• •• •^^^"^"''7— R e t i c u 1 u nn 



,o- 



P^ig. 10 Section through the posterior semicircular canals in a human fetus 

 52 mm. long (Carnegie Collection, No. 96). Enlarged 100 diameters. Here the 

 replacement of precartilage by reticulum has been more active than that of 

 cartilage by precartilage so there remains only a narrow zone of the latter. The 

 reticulum begins to show an alteration in its trabeculae. Due to the retraction 

 and rearrangement of the protoplasm of some of the trabeculae there results a 

 coalescence of adjacent intertrabecular spaces. There are thus formed larger 

 fluid spaces that are devoid of traversing trabeculae. As yet there is no 

 perichondrium. 



from the epithelial wall of the labyrinth to the true cartilage. 

 It will be seen that the membrana propria consists of a narrow 

 meshed syncytium, such as is found in embryonic fibrous con- 

 nective tissue, and constitutes a supporting coat for the epithelial 

 wall of the semicircular duct. The main part of the periotic 

 connective tissue consists of a wide-meshed reticulum and arbor- 



