500 



EMBRYOLOGY. 



The throe semicircular canals do not lie exactly in the middle of the 

 cavities of the embryonic cartilage containing the gelatinous tissue, 

 but are so situated that their convex borders are in almost immediate 

 contact with the cartilage, whereas their concave sides are separated 

 from it by a thick layer of gelatinous tissue. The latter is differen- 

 tiated into three layers : into a middle portion, in which the gelatinous 

 intercellular substance is greatly increased in volume, and becomes at 

 the same time more fluid, and into two limiting layers, which are 

 converted into fibrous connective tissue. One of the two [the inner] 

 is intimately united to the epithelial tube, for the nutrition of which 



dc 



dc 



Cdc 



kk 



dc 



kl- 



nc 



nc gs ns 



S U 



Fig. 281. Section through the cochlea of a Sheep embryo 7 cm. long, after BOKTTCHER. 

 Magnified 20 diameters. 



/,/, Cartilaginous capsule of the cochlea ; S, sacculus with the nerve (ns) distributed to it ; 

 U, utricle ; gs, ganglion connected with the cochlear nerve (nc) and sending nerve-fibres (ns) 

 to the sacculus ; gsp, ganglion spirale ; dc, ductus cochlearis ; C, CORTI'S organ ; g, gelatinous 

 tissue in the periphery of the ductus cochlearis ; x, more compact connective-tissue layers. 



it provides by means of a close network of blood-vessels distributed 

 through it ; the other [the outer] lies on the inner surface of the 

 cartilaginous envelope and becomes its perichondrium. 



The gelatinous tissue of the middle layer is of only short duration. 

 It soon shows signs of degeneration. The stellate cells become filled 

 with fat granules in the vicinity of their nuclei and in their long 

 processes ; later they disintegrate. In the gelatinous matrix there 

 are formed, by a continually advancing process of softening, cavities 

 filled with fluid. These increase in size and then become confluent, 

 until finally there has arisen between the connective-tissue membrane 

 of the semicircular canals and the perichondrium, in place of the 



