366 .MICROSCOPIC ANATOMY OF THE 



border and passes over into the neuro-epithelium. In the 

 latter we can distinguish two kinds of cells: 1, supporting 

 cells; and 2, hair cells. 



1. The supporting cells are long structures somewhat 

 widened at each end and split at the lower extremity. The 

 oval nucleus lies, as a rule, in the lower half of the cell. 



2. The hair cells are cylindrical cells which do not occupy 

 the whole thickness of the epithelial layer. The thickened, 

 bulged end, which contains a spherical nucleus, reaches only as 

 far as the middle of the layer. The free upper end of the cell 

 presents a cuticnlar border with a number of fine hairs, which 

 are shorter in the macula than in the crista. The hair cells are 

 elements which are in close contact with the sensory nerves. 

 The relation of the nerve fibres to the hair cells is as follows : 

 The nerve fibres break through the basal membrane, lose their 

 medullary sheaths, and at the bases of the hair cells break up 

 into three or four branches, which go to form a horizontal 

 plexus (stratum plexiforme). These surround the hair cells 

 like the calyx of a flower, and give off ascending branches, 

 which, however, do not reach the surface. In this way one 

 branch usually comes in contact with many hair cells (Retzius, 

 Ramon y Cajal, and others). 



The macula? acusticae are covered by a layer of soft gelatin- 

 ous substance, the so-called otolith membrane, which encloses 

 numerous small prismatic otoliths (statoliths, otokonien crys- 

 tals). These consist of calcium carbonate. The otolith mem- 

 brane is to be regarded as a cuticular structure. 



In the ampullaB we find on each crista a conical structure, 

 the cupola, which corresponds with the otolith membrane. 

 This is seen plainly in fixed preparations, where the semifluid 

 substance between the auditory hairs is coagulated. In the 

 neighborhood of the cristse and macula3 the whole wall of the 

 sacculus utriculus and canals is distinctly thicker, owing to 

 the increased thickness of the connective-tissue sheath and 

 basal membrane. 



