8. 



GEORGE L. STREETER 



capsule into a true cartilage with a characteristic tinctorial re- 

 action of its matrix is not completed until the embryo attains 

 a length of 30 mm. Thus in embryos between 14 and 30 mm. 

 long the otic capsule consists of a tissue in an intermediate con- 

 dition between condensed mesenchyme and cartilage. This inter- 



Otic cap s u le 



Ec t o de rm 



Skull 



—D. sc.p&st. 



Sinus t r. 



N. IX 



Fig. 4 Section through the region of the otic capsule in a human embryo 15 

 mm. long, (Carnegie Collection, No. 719). Enlarged 66.6 diameters. The 

 epithelial portions of the labyrinth are shown in solid black and it will be noted 

 that they are in direct contact with the substance of the capsule; there is as yet 

 no periotic reticular tissue. The section passes through the superior and pos- 

 terior semicircular ducts and through the utricle near its junction with the 

 crus commune. 



mediate form is known as precartilage. It constitutes the second 

 of our three stages of cartilaginous growth. 



The general form and relations of the otic capsule at the begin- 

 ning of its conversion from condensed mesenchyme into precar- 

 tilage is shown in figure 4, which represents a horizontal section 

 through this region in a human embryo 15 mm. long (Carnegie 



