896 OF SENSATION, AND THE ORGANS OP THE SENSES. 



the Cochlear nerve. 1 This nerve passes out from the modwlus into a series of 

 anastomosing canals excavated in the osseous lamina spiralis; and it there 

 comes into relation with a band of vesicular substance, which lies near the edge 

 of the lamina along its whole length. The component vesicles are elongated, 



Fig. 219. 



A highly magnified view of a small piece of the Lamina Spiralis, showing the manner in which the nerves 

 leave their Neurilemma as they anastomose; the natural size of the piece is seen on the side of the figure; 1, 

 portion of the auditory nerve ; 2, 2, osseous canals in the zona ossea of the lamina spiralis ; 3, 3, anastomoses 

 in the zona mollis ; 4, 4, the neurilemma leaving the nervous loops, and interlocking to form the layer of the 

 zona memhranacea. 



having a central and a peripheral extremity ; by the former they are connected 

 with the fibres of the cochlear nerve, the connecting filaments being destitute (as 

 elsewhere) of the double contour, and being very fragile ; and by the latter they are 

 similarly connected with the fibres which issue forth from the osseous lamina, to 

 be distributed upon its membranous continuation. These fibres form fasciculi, 

 which traverse the membranous lamina nearly parallel to each other, and anas- 

 tomose continually with one another, in such a manner as to present the appear- 

 ance of looped terminations. According to Corti, however, the fibres really 

 pass on further, losing their double contour, and becoming gradually incorpo- 

 rated, as it were, with the surrounding tissue. 3 



899. In order to gain any definite idea of the uses of different parts of the 

 Ear, it is necessary to bear in mind, that sounds may be propagated amongst 

 solid or fluid bodies in three ways : by reciprocation, by resonance, and by con- 

 duction. 1. Vibrations of reciprocation are excited in a sounding body, when 

 it is capable of yielding a musical tone of definite pitch, and another body of 

 the same pitch is made to sound near it. Thus if two strings of the same length 

 and tension be placed along-side of each other, and one of them be sounded with 

 a violin bow, the other will be thrown into reciprocal vibration ; or if the same 

 tone be produced near the string in any other manner, as by a flute or a tuning- 

 fork, the same effect will result. 2. Vibrations of resonance are of somewhat 

 the same character ; but they occur when a sounding body is placed in connec- 

 tion with any other, of which one or more parts may be thrown into reciprocal 

 vibration, even though the tone of the whole be different, or it be not capable 



1 See Kolliker and Siebold's "Zeitschrift fur Wissenschaftliche Zoologie," 1851, band 

 iii. heft 1. 



2 Such, also, is the account of their termination given by Messrs. Todd and Bowman, 

 " Physiological Anatomy," p. 467, Am. Ed. 



