The Nature of the Tectorial Membrane 163 



of the energy to the cndolymph, the reduction of amplitude, as well as 

 the increase of the force, depends not only upon the lever arrangement 

 of the ossicles, but upon the tensity of the tympanic muscles and the 

 pressure of the air in the tympanic cavity. Therefore, the wave motions 

 imparted to the endolymph by the basis of the stapes correspond to the 

 atmospheric sound waves, of which they are transformations, but re- 

 semble them only in frequency of vibration. The quality of the motion 

 imparted to the endolymph depends of course upon the quality or form 

 of the atmospheric waves acting upon the tympanic membrane, but the 

 quality of the two may not be identical in detail. While the canals of 

 the cochlea are probably entirely filled with endolymph normally, and 

 under a pressure which depends largely upon the blood pressure of the 

 different conditions of the body, the membrane over the fenestra cochleie 

 (rotunda) and the direct continuation of the endolymph of the cochlea 

 with that of the vestibule are considered sufficient to allow compensation 

 for the incompressibility of the fluid and to allow propagation of the 

 motion in the form of true compression waves. Pressure applied by the 

 stapes to the endolymph in the cochlea may not only be compensated or 

 relieved by the membrane below and by the ductus reuniens connecting 

 it with the sacculus, utriculus and semi-circular canals, but, by way of 

 the sacculus, such periodic pressure may be compensated through the 

 ductus endolymphaticus into the cranial cavity. Furthermore, the layer 

 of softer tissue between the epithelium lining the scalge and the solid 

 walls of the bony labyrinth may aid in maintaining the form of the 

 wave motion. Therefore there is reason to conclude that the motions 

 imparted by the stapes at the basal end of the cochlear coil are propa- 

 gated in the endolymph toward the apex of the cochlea in the form of 

 compression waves, however short, with longitudinal direction and trans- 

 verse vibration. The waves are very probably similar in many respects 

 to pulse waves. 



(7) That the agitation of the hairs of the hair cells is brought about 

 through the activity or actual movements of the tectorial membrane 

 induced by the wave motion transferred to the endolymph is suggested 

 by the peculiarities of that membrane. 



. (a) It is in the logical position for such action. It lies above the hair 

 cells adjacent to the portion of the endoh-mph to which the waves are 

 first imparted by the basis of the stapes. The basilar membrane is 

 situated below the tectorial and is both covered and obstructed. 



(6) In the mammalia and in all animals possessing it, the tectorial 



