KELATIONS OF AUDITORY NERVE TO ORGAN OF CORTI. 169 



by two roots from the medulla oblongata. One of these is 

 composed of delicate fibres, and its ganglionic nucleus of origin 

 (central auditory nucleus of Stieda) consists of small ganglionic 

 masses in the floor of the fourth ventricle. The second root, 

 which, according to Stieda, contains remarkably thick axis- 

 cylinders thicker than those of any other nerve arises from 

 a special large-celled ganglion of origin situated in the crus 

 cerebelli ad medullam oblongatum (lateral auditory nucleus of 

 Stieda). Deiters (16) also has described and depicted this nu- 

 cleus, without, however, recognizing the origin of the auditory 

 nerve from its ganglion cells. Further details, together with 

 the literature of the subject, will be found in Stieda's treatises 

 (loc. cit.}. The thick-fibred root, like a posterior root of a spinal 

 nerve, has a small ganglion upon it soon after its emergence 

 from the medulla. 



The two roots speedily coalesce to form a common trunk, the 

 primitive fibres of which were not unfrequently observed by 

 Czermak (11) to divide and branch, and are probably to be re- 

 garded as fasciculi of primitive fibrils, possessing only medullary 

 sheaths, (II. 2, voL i., p. 158, of this work,) since it is impossible 

 to demonstrate the presence of the sheath of Schwann in them. 

 In the internal auditory meatus the trunk divides into two 

 branches, the ramus vestibularis and the ramus cochlearis. 

 The former again presents a small ganglion, the intumescentia 

 gangliformis of Scarpa, and breaks up into the rami ampul- 

 lares and reticularis, and the ramus sacculi. The much stronger 

 ramus cochlearis also gives a small fasciculus to the septum 

 membranaceum utriculi et sacculi (Henle, 26), and to the ma- 

 cula cribrosa quarta of Reichert (45), which, however, is con- 

 tested by Middendorp (40), and then passes through the tractus 

 spiralis foraminulentus directly to the first turn of the lamina 

 spiralis and the modiolus, from whence it gives off branches to 

 the remaining coils of the spiral lamina. Before, however, the 

 fasciculi of fibres enter the lamina spiralis, the branches col- 

 lectively traverse the ganglion spirale, occupying the canalis 

 ganglionaris at the base of the lamina spiralis. Probably a 

 bipolar ganglion cell is here intercalated in the course of each 

 nerve fibre. Numerous ganglion cells are similarly interposed 

 in the principal trunks, as well as in the ramus vestibularis, 



