126 



THE EAR. 



of Corfci. In most animals they are less grouped together and more distributed 

 along the length of each cell of Deiters (fig. 139), but with the same spiral arrange- 

 ment and in the same relative position. 



Vessels of the cochlea. The branches of the internal auditory artery to the 

 cochlea, twelve or fourteen in number, arising at the bottom of the internal auditory 

 meatus, traverse small canals in the modiolus and bony lamina spiralis, and also pass 

 to the outer wall of the cochlea, forming at the root of the septum, between the 

 turns of the cochlear tube a spirally-arranged glomerulus-like arterial plexus, 

 which sends vessels to the subjacent stria vascularis and to the periosteum lining 

 the adjacent scalse (Schwalbe). From this plexus offsets are distributed in the 

 form of a fine network on the periosteum, but the vessels do not anastomose across 

 the membrana basilaris. The bony cochlea also receives through the fenestra rotunda 

 a twig from the stylomastoid branch of the occipital artery. 



The veins of the cochlea issue from the grooves of the cochlear axis, and join the 

 veins of the vestibule and semicircular canals at the base of the modiolus. A small 

 sinus-like vein passes through the aqueductus cochleae, from the lowermost turn of 

 the cochlear tube, and joins the commencement of the internal jugular vein. 



Development of the organ of Corti. The organ of Corti is at first com- 

 posed of columnar epithelium-cells forming part of the layer of epithelium which 



membrana, inner 



tectoria hair-cell outer hair-cells 



duct of cochlea 

 inner hair-cell outer hair-cells 





inner rod vas spirale outer rod 



Figs. 147 and 148. Two STAGES IN THE DEVELOPMENT OF THE ORGAN OP CORTI OF THE CAT. 



(GL Retains.) 



In the preparation represented in fig. 147 the hair-cells are differentiated ; in that shown in fig. 148 

 the rods of Corti are also beginning to be formed, and the nerve-fibres have reached the organ of Corti, 

 and are already running spirally below the hair-cells. 



lines the whole of the membranous labyrinth. After a time certain of these cells 

 begin to be differentiated and become distinguishable from the rest as the inner and 



