610 PHYSIOLOGY 



with t he cochlear branch of the auditory nerve ,md traverse the foramina in the spiral 

 lamina alongside the outgoing nerve fibres, to join with several arteries which run 

 round the inside of the cochlea. The largest of these vessels is found in the scala media. 

 Minute branches pass from these to the hair-cells, etc. ; the venous blood being collected 

 in corresponding veins. (2) The outer wall of the scala media is highly vascular, a 

 network of capillaries lying under the epithelium. It is probable that oxygen and 

 food pass by osmosis into the endolymph through the epithelium and that waste products 

 are removed in the same way. (3) Perilymph excreted in the utricle and saccule pass 

 up the scala vestibuli to the top of the cochlea, then through a minute pore called 

 the helicotrema into the scala tympani below and back along this canal to escape 

 from the internal into the middle ear by a minute opening below the round window. 

 The helicotrema is apparently large enough to insure- that the mean pressure in the 

 scala vestibuli shall be equal to that in the scala tympani, but not so large that the 

 momentary differences in pressure, caused by the movements of the stapes, are obli- 

 terated. 



