ORGAN OF HEARING. 



Ml 



to enable me to say positively which description 

 is the most correct.* 



The nervous fibrils of the cochlea, according 

 to Breschet, traverse the osseous zone of the 

 spiral lamina under the form of cylindrical 

 bundles, which, in the middle zone, become 

 flat, and anastomose by loops. These loops 

 are intermingled with small osseous particles. 

 Near the outer margin of the middle zone, the 

 neurilemma leaves the nervous filaments, and 

 goes to form the framework of the membraneous 

 zone, whilst small globules are seen irregularly 

 disseminated around the convexity of the loops 

 which the filaments form by their anastomoses. 

 All this, however, is not so unequivocally dis- 

 tinct as Breschet pretends. What I have been 

 able to see in regard to the termination of the 

 nerves on the spiral lamina, is simply this : 

 The tubular structure of the nervous filaments 

 ceases, among grains of nervous matter ar- 

 ranged into a sort of expansion. There is 

 nothing that can be called a termination in 

 loops. Mueller thinks the nervous fibrils do 

 not form loops in the bird's cochlea. " But," 

 says Mueller, " it is of no consequence, in the 

 present state of the physiology of the nerves, 

 whether the nerves of sensation form at their 

 terminations loops or not." 



Treviranusf found a papillary termination 

 of the nervous filaments, not only in the retina, 

 but also in the nervous expansions of the ear 

 and nose. The papillae of the auditory nerve 

 he saw on the spiral lamina of the cochlea in 

 young mice. The osseous part is entirely 

 covered with filamentous papillae, lying close 

 together. Gottsche also found the ends of the 

 nerves of the cochlea in hares and rabbits club- 

 shaped. In the hare, the nervous cylinders ter- 

 minate in an oval knob. 



The following figures from Breschet illustrate 

 his views of the mode of termination of the 

 nervous filaments of the cochlea. 



JVg. 241. 



The cochlear nerve entirely isolated. (Magnified.) 

 a, a, a. trunk of the nerve ; b, b, b. its filaments 

 in the osseous zone of the spiral lamina ; c, c, c. the 

 anastomoses in the middle zone. 



* In the sheep I have found the division of the 

 auditory nerve corresponding to the first description 

 given above. 



t Beitrage, &c. Isten Bandes 2tes Heft. Neue 

 Untersuchungen ueber die organischen Elemente 

 der thierischen Koerper, p. 55. Bremen, 1835. 



A, a tmall piece of the spiral lamina, natural size, 

 as seen from the surface corresponding to the scala 

 vestibuli. 



B, the same part considerably magnified to show 

 the globular structure (?) of the nerves and the mode 

 in which the neurilemma leaves them at the place 

 where they form their anastomoses. 



a. Portion of the trunk of the cochlear nerve ; 



b. fasciculi lodged in the osseous zone of the cochlea ; 



c, c. anastomoses in the middle zone ; d, d, d. the 

 neurilemma leaving the nervous loops, interlacing 

 and forming the basis of the membraneous zone. 



As to the mode in which the nervous fila- 

 ments enter and terminate in the membraneous 

 labyrinth. The nervous filaments, according 

 to Scarpa, before penetrating the vestibule of 

 the small bony canals, lay aside their thicker 

 sheath, and become softer and whiter. The 

 filaments expand on the parts for which they 

 are destined, appear to form a network, and, 

 having penetrated into the interior, are resolved 

 into a nervous pulp which lines the inner sur- 

 face. Scarpa compares this nervous expansion 

 in the saccule to the retina. 



According to Breschet's account, the nervous 

 filaments, in penetrating into the interior of the 

 different membraneous pouches, are accompa- 

 nied by a sheath furnished by the pouch itself, 

 which is folded inwards, and accompanies them 

 until these filaments spread themselves out. 

 Hence it is that, at the entrance of the nerves, 

 the walls of the pouch are always thicker, and 

 form a more or less considerable projection in 

 the interior. This prominence is slight in the 

 saccule and common sinus, but very well 

 marked in the interior of the ampullae, where it 

 forms a sort of incomplete septum across ; a 

 structure which is small in man and the mam- 

 mifera, but very much developed in birds and 

 the higher reptiles. 



At those prominences the nervous filaments, 

 says Breschet, present anastomosing loops, and 

 the neurilemma leaving them to be incorporated 

 with vessels, and thus to form the framework 

 of the membraneous labyrinth, the nervous 

 globules come into immediate contact with the 

 mass of calcareous matter. 



What I have said of Breschet's account of 



