302 ESSENTIALS OF ZOOLOGY 



channels communicate at the distal end of the cochlea. At 

 the proximal end one of these perilymph canals opens on the 

 upper or vestibular side, and is called the scala vestibuli ; the 

 other opens on the ventral side near to the fenestra rotunda, 

 and is called the scala tympani. The cochlear duct is often 

 termed the scala media. It is in section a triangular-shaped 

 sac. One limb of the triangle is applied, as has been said, to 



Vestibular membrane 



Osseous spiral 

 lamina 



Cochlear nerves 



Sulcus spiralis internus 

 Membrana tectoria 



Stria vascularis 



Sulcus spiralis 

 externus 



Crista basilaris 



Basilar membrane 



Spiral organ 

 (From ' Gray's Anatomy.') 



FIG. 141. A still more magnified view of the cochlea to indicate details of 

 ( structure of the organ of Corti. 



the bony side of the canal ; the upper side is bathed externally 

 by the fluid of the scala vestibuli, and the lower limb by that 

 of the scala tympani. These free membranes meet and are 

 supported by the shelf or spiral lamina. Between the spiral 

 lamina and the wall the lower membranous part of the cochlea 

 has been greatly modified, forming the organ of Corti, and it 

 is supplied by the branches of the cochlear nerve. The organ 

 of Corti consists of sensory cells ending in hairs and divided 

 into a row of single cells internally, and a row of three or four 

 cells externally, by two stiff supporting cells, called the rods of 

 Corti, and all based on an elastic fibrous layer, the basilar 



