AUDITOR? ORGAN. 365 



the ductus ulriculo-saccularis. The sacculus communicates by 

 means of the ductus reuniens (Henseni) with a long spiral 

 structure, the cochlea (ductus cochlearis). The utriculus, on 

 the other hand, is connected with the three semicircular canals, 

 each of which is dilated to form an ampulla at its point of com- 

 munication with the utriculus. 



These membranous structures, taken together, form the 

 membranous labyrinth, which is surrounded by firm bony 

 labyrinth. The membranous labyrinth contains a fluid, the 

 endolymph, while its outer surface is bathed in the perilymph 

 which fills up the space between the bony and membranous 

 labyrinths. 



(1 ) Sacculus, Utriculus, and Semicircular Canals. 



All of these parts possess a somewhat similar structure, 

 which in comparison with that of the cochlea is quite simple. 

 They all incompletely fill the bony spaces in which they lie, and 

 only in certain places are fixed to the periosteum. The free 

 spaces are traversed by connective-tissue strands (ligamenta 

 sacculorum et ductuum), which, on the one hand, are fastened 

 to the wall of the canal, and, on the other, to the periosteum. 

 These strands are covered with a layer of flat epithelial cells 

 similar to those of the periosteum and labyrinth. 



The walls of these sacs and canals consist of three layers, 

 namely, a connective-tissue sheath rich in elastic fibres, n 

 structureless basal membrane, and an epithelial layer. The 

 last consists of a single layer of flat epithelium. 



Along the concave side of each semicircular canal there is a 

 line, the so-called raphe, where the cells increase considerably 

 in height. Also in the ampullae the cells bordering on the 

 crista3 acusticas are cylindrical, and form the plana semi- 

 lunata. 



Where the auditory nerve ends, the epithelial layer is more 

 complicated. In the sacs there are found the maculce acusticce, 

 and in the ampullae the cristce acusticce. The low epithelium 

 becomes in these regions much higher. It shows a cuticular 



