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MANUAL OF PHYSIOLOGY. 



structures, and the general epithelium lining the membranous 

 labyrinth. The mesoblast supplies the surrounding firmer struc- 

 tures, such as the fibrous substance of the inner ear, and the bony 

 parts in which the organ lies. The auditory nerve grows as a 

 bud from the neural tissue forming the hind-brain, and connects 

 it to the delicate specialized auditory cells. 



The process begins by the appearance of a depression of the 



FIG. 296. 



V.B 



Transverse section through the head of a foetal sheep in the region of the hind-brain. 

 (Boettcher.) HB. Hind-brain, cc. Canal of the cochlea. RC. Recessus vestibuli. VB. 

 Vertical semicircular canal. GC. Auditory ganglion. G'. Auditory nerve. N. Connec- 

 tion of auditory nerve to the hind-brain. 



general epiblast covering the head, which soon forms a tubular 

 diverticulum, lying in the mesoblast at the side of the hind- 

 brain. 



This diverticulum becomes separated from the epiblast by the 

 obliteration of its outer extremity, which united it to the super- 

 ficial epiblast, and is then converted into a cavity and receives 



