SENSE OF HEARING. 



427 



best seen in the lamina spiralis of the cochlea, and its membranous prolon- 

 gation. Much diversity exists, however, as to the interpretation of the ap- 



[Fig. 187. 



[Fig. 188. 



A highly magnified view of a small piece of the Lamina Spiralis, 

 showing the globular structure of the Nerves, and the manner in 

 which they 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 membranacea.] 



Plexiform arrangement of the 

 cochlear nerves seen in the basal 

 coil of the lamina spiralis, treated 

 with hydrochloric acid. There 

 are no ganglion globules in this 

 plexus, which consists of tubular 

 fibres, a. Twig of cochlear nerve 

 in the modiolus, its fibres diverging 

 and reuniting in 6, a band in the 

 plexus taking a direction parallel 

 to the zones. From this other 

 twigs radiate, and again and again 

 branch and unite as far as the mar- 

 gin of the osseous zone c, where 

 they terminate. From the sheep. 

 Magnified 30 diameters.] 



pearances there seen ; some observers affirming that there are no free or 

 papillary terminations, and that the nervous fibres all return by loops ; whilst 

 others state that the papillae are clearly to be distinguished. The fact appears 

 to be that, as in the retina, the fibres do form a minute plexus ; but that fibres 

 are connected with this, which end, or rather commence in papillae. The 

 Auditory nerve is also very minutely distributed on the membrane lining the 

 vestibule and semicircular canals; and in the ampullae or dilated extremities 

 of the latter, there are little projections of this membrane internally, which 

 are largely supplied with nerves. 



560. 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 

 conduction. 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 vibra- 

 tion ; 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 sound- 



