588 SEMICIRCULAR CANALS. [sect. 233. 



and form small arteries and veins, which are distributed in numer- 

 ous capillary networks upon the fibrous and vitreous coats, and 

 most abundantly in the neighbourhood of the terminations of the 

 nerves. Of such terminations, only those of the auditory nerve 

 are known ; this nerve gives off the nervus vestibuli for the supply 

 of the three membranous canals, and of the sacculus ellipticus, 

 while the round sacculus is supplied by a branch from the cochlear 

 nerve. In the canals, the nerves are distributed only upon the 

 ampullae, in each of which, as Steifensand has shown, they enter 

 into an incurvation or duplicature of its wall upon the concave 

 side of the canal, and in this way a transverse projection is pro- 

 duced on the inner aspect of the wall, occupying about one-third 

 of the circumference. The nerves divide within these folds, first into 

 two main branches, which drverge towards the two borders of 

 them, and then break up in the vitreous coat of the ampulla into 

 dense tufts of smaller branches, which anastomose with each other 

 in various ways, and form fine twigs containing from two to ten 

 primitive fibres, o - 001'" to coo^'" thick; these twigs pass through 

 the membrane of the ampullae and end in the epithelium, which is 

 here thicker than elsewhere (Reich, M. Schultze, and myself) ; 

 Fig. 239. their mode of termination is not yet suf- 



ficiently understood. The distribution 

 of the nerves is similar in the saccules, 

 except that it occupies a larger space, and 

 the projection of the wall in which the 

 nerves are situated is much less marked 

 here than in the ampullae. At the place 

 cuxX sv ^rai! ec « on fib™L S co ; ;t of the nervous expansion, there exists in 

 ^ZSVepith h eiZ se Fr°om each of the saccules a chalk-white and 



the calf. Mag. 250 diameters. sharply bounded Spot, readily visible to 



the naked eye ; it is fixed on the internal wall of a very clear 



membrane, o*oi'" thick, perhaps of the nature of an epithelium. 



Fig. 240. This is the so-called otoconia of Breschet, or otolith, and 



r , f is composed of innumerable round elongated corpuscles, 



% °o° ) !) often in the form of double pointed, probably six-sided, 



f) 9 W% columns; these particles are suspended in a homoge- 



otoiithesfrom ucous substance, and measure 0*0004'" to 0'005'" in 



the internal ear 1 , i t ,i i /// . ,,,  



ofthecaif. Mag. length, and the larger ones are cooi to 0*002 m 

 breadth. They consist of carbonate of lime, and when 

 this is removed, they leave behind, it is said, a small quantity of 

 organic matter, but I have not yet succeeded in observing it. 



