28 



THE HISTOGENESIS AND GROWTH OF THE OTIC CAPSULE AND ITS 



Epithelium 



Reticulum 



Precartilage 



cartilage from the inner zone of temporary precartilage surrounding the semi- 

 circular ducts. The true cartilage has developed a considerable amount of matrix 

 separating the encapsulated nuclei or cartilage cells. The margins of the capsules 

 stand out as sharp refractive lines. The matrix lying between the capsules is 

 slightly opaque and is beginning to take a differential stain. A narrow interme- 

 diate or transition zone separates the true cartilage from the precartilage; this zone 

 is characterized by the presence of flattened and partially collapsed capsules between 

 which there is very little or no matrix. The refractive margins of these over- 

 lapping, incomplete capsules give the appearance of wavy lines that run parallel 

 with the margin of the canal. The same appearance is not seen in other regions of 

 .the otic capsule in younger stages, where 

 precartilage is differentiating into carti- 

 lage. 



In the process of cartilage differen- 

 tiation in most parts of the otic capsule 

 there is considerable intercapsular mate- 

 rial at the time the margins of the cap- 

 sules become conspicuous. The capsules 

 are separated by the matrix-forming syn- 

 cytium. Thus, there are not the con- 

 spicuous wavy lines due to overlapping ^ .^ & ~. 

 capsules, such as characterize the inter- 

 mediate zone. The transition between 

 this zone and the true cartilage on one 

 hand and the temporary precartilage on 

 the other is quite abrupt in both in- 

 stances. On entering the zone of pre- 

 cartilage there is found between the 

 nuclei, instead of the wavy refractive 

 capsular lines, a framework having more 

 the character of a granular syncytium, 

 with only here and there the suggestion 

 of a beginning capsule. This, it will be 

 remembered, is a condition the true car- 

 tilage exhibited in its earlier period. It 

 is the intermediate zone to which we 

 should address our especial attention, 

 and it is this zone that moves outward 

 as the cartilaginous canal widens. 



Text-figure 1 shows a section 

 through these zones in a fetus of about 

 the same age as the one just described. 

 This section is taken through the lateral canal of a fetus 33 mm. crown-rump 

 length (Carnegie Collection, No. 145). The intermediate zone stands out con- 



Cartilage 



FIG. 1. Detail of a section through the lateral semicircu- 

 lar canal in a human fetus 33 mm. long (Carnegie 

 Collection, No. 145, slide 7, row 1, section 3). The 

 section is 5(V thick and is enlarged 376 diameters. 

 It shows the epithelial wall of the semicircular duct 

 and the tissue zones that intervene between it and 

 the cartilaginous capsule. In the outer part of the 

 pre-cartilage zone is an intermediate area which is a 

 transitional form between cartilage and precartilage. 

 It is characterized by the scant amount of matrix and 

 the incomplete and flattened condition of the capsule. 



