716 THE EAR 



Those veins coming from the wall of the scala tympani unite to form 

 superior and inferior spiral veins in the inner wall of the scala tympani. 

 These vessels chiefly empty into the vena aqueductus cochlea which 

 finds its way through the aqueduct to the internal jugular vein. Other 

 branches from the interior of the cochlea unite to form the central vein 

 of the cochlea, which becomes the chief radical of the internal auditory 

 vein, and thus enters either the transverse or inferior petrosal sinus. 



The veins from the utricle and semicircular canals mostly enter the 

 vena aqueductus vestibuli, which follows its aqueduct to the superior 

 petrosal sinus. 



It will be perceived that the blood has three chief avenues of exit from 

 the labyrinth : 1, by the vena aqueductus vestibuli ; 2, by the vena aque- 

 ductus cochlea?; and, 3, by the internal auditory vein. The greater 

 portion of the blood pursues the second course and thus finds its way to 

 the internal jugular vein, the smaller remainder entering the petrosal 

 sinuses by one of the other two avenues. 



Lymphatics. The internal ear contains relatively few lymphatic 

 vessels but is richly supplied with broad lymphatic spaces. Anastomosing 

 vessels are found in the periosteum and membranous wall of the laby- 

 rinth. These communicate with the perilymph spaces between the peri- 

 osteum and the membranous wall in the vestibule, and with the vestibular 

 and tympanic scalse in the cochlea. The perilymphatic spaces are con- 

 nected with the subdural space of the meninges by means of lymphatic 

 channels in the aqueductus cochlea?. The perilymph of the vestibule also 

 communicates with the subdural space through vessels which follow the 

 sheaths of the nerves. 



The endolymph cavities of the several divisions of the membranous 

 labyrinth communicate freely with one another; by means of the ductus 

 endolymphaticus a connection is also established though the aqueductus 

 vestibuli with the subdural space, the blind terminal saccule of this 

 canal, the saccus endolymphaticus lying upon the posterior surface of 

 the petrous bone and in contact with the dura mater. 



FUNCTION OF THE COCHLEA 



The cochlea is the essential organ of hearing. The fundamental struc- 

 ture concerned in audition is the spiral organ of Corti. The physiology 

 of sound perception involves proximally the stimulation of the hair cells 

 of Corti's organ by the tectorial membrane. This membrane is thrown 



