EXCAVATION OF THE CARTILAGINOUS OTIC CAPSULE 11 



that the precartilage becomes cartilage. In embryos 30 mm. 

 long the greater portion of the otic capsule reacts tinctorially and 

 has the histological character of young cartilage. With this 

 stage we reach the third and final phase of the process with which 

 we are dealing. The further changes from younger cartilage to 



K:m) \^a 



Fig. 6 Characteristic precartilage cells showing the manner in which spaces 

 become enclosed around them, eventually becoming encapsulated cells of true 

 cartilage. Enlarged 950 diameters. Group A is from the otic capsule of an 

 embryo 17 mm. long (Carnegie Collection, No. 296) ; Group B is from an embryo 

 24 mm. long (Carnegie Collection, No. 455) ; and Group C is from an embryo 23 

 mm. long (Carnegie Collection, No. 453). 



older cartilage, and the conversion of cartilage into bone, are 

 doubtless a continuation of the same general process but in the 

 present paper they will not be taken into consideration. 



PERIOTIC RETICULUM 



It has been pointed out elsewhere by the writer^ that there 

 is derived from the condensed mesenchyme surrounding the otic 

 capsule not only the cartilaginous capsule but also the periotic 



' Streeter, G. L. The development of the scala tympani, scala vestibuli and 

 perioticular cistern in the human embryo. Am. Jour. Anat., vol. 21, 1917. 



