Chap.XLI.] 



THE INTERNAL EAR. 



323 



The structure of the wall is the same in the semi- 

 circular canals, utricle and saccule. The above-men- 

 tioned fibrous ligaments of the periosteum form an 

 outer coat; inside this is a glassy- looking tunica 

 propria. At one side (the one away from the bone) 

 this tunica propria forms numerous papillary projec- 

 tions. The internal 

 surface of the mem- 

 brane is covered with a 

 single layer of poly- 

 hedral epithelial cells. 



464. Each of the 

 branches of the nervus 

 vestibuli i.e., one for 

 the saccule, one for the 

 utricle, and three for 

 the three ampullae 

 possesses a ganglionic 

 swelling. The nerve- 

 branch, having passed 

 through the membra- 

 nous wall, enters 

 special thickenings of 



the tunica propria, on pig> 162 ._ From a Transverse Section 

 that part of the mem- through the Macula Acustica of the 

 brailOUS wall next to Utricle of the Labyrinth of a Guinea. 



the bone ; in the sac- 

 cule and utricle the 

 thickening is called 

 macula acustica, in the 

 ampullae crista acustica 



(Fig. 162) (M. Schultze). This thickening is a large 

 villous or fold-like projection of the tunica propria, 

 into which pass the nerve fibres of the several 

 branches. These fibres are all medullated nerve- 

 fibres, and, ascending towards the internal or 

 free surface of that projection, form a plexus. In 



:, Medullated nerve fibres, forming plex- 

 uses; b, nuclei of the membrane; e, 

 the sensory epithelium (diagrammatic) ; 

 the spindle-shape^ sensory-cells possess 

 long auditory hairs projecting between 

 the conical epithelial cells beyond the 

 free surface. (Atlas.) 



