vi] Anatomical Evidence i'/ //(in/in;/ Function 167 



First, concerning the peripheral and lower neurones; the connections of these are of 

 the greatest possible complexity, and much study has been needed for their unravelment ; 

 however, from the researches on degeneration carried out by von Monakow, Ferrier and 

 Turner, and Wyrubow, the developmental studies of Flechsig and Bechterew, and those of 

 von Kolliker, Ramon y Cajal, Held and others, on histological lines, we conclude that the 

 elucidation of the course and connections of these lower neurones is now practically com- 

 plete and that the track travelled by auditory impulses is as follows. 



From the organ of Corti they pass along the cochlear nerve to the ventral and dorsal 

 cochlear nuclei, the latter of which is better known by the name tuberculum acusticum. 

 This constitutes the first link in the chain. 



From here, some fibres of the second system of neurones are led, by way of the striae 

 medullares or striae acusticae and corpus trapezoideum, to the superior olivary bodies on 

 both sides and to nuclei in the trapezoid body; while others proceed, by way of the lem- 

 niscus lateralis, to the posterior corpora quadrigemina and the middle geniculate bodies. 



Lastly, fibres leave these bodies to pass through the retrolentiform portion of the internal 

 capsule and make their way along the corona radiata to the temporal cortex. 



For proof of the correctness of this statement in so far as the two lower links in this 

 chain are concerned the reader is referred to special works ; here allusion need only be 

 made to the upper link. As Barker remarks, no better demonstration of this section can 

 be obtained than by an examination of foetal brains, and in the illustrations published 

 by Flechsig, and by Cecile and Oskar Vogt, these fibres are indicated with unsurpassed 

 clearness. I have already mentioned that these fibres pass out through the retrolentiform 

 portion of the internal capsule, and I can now add that, according to Flechsig, they are 

 divisible into two bundles, one of which ascends near the external capsule and gains the 

 auditory cortex from the posterior and superior side, while the other courses for some 

 distance in company with the occipito-thalanu'c radiations, and then passing behind and 

 below the fossa Sylvii pierces the bases of the second and third temporal convolutions to 

 gain the transverse temporal gyri. The information derived from a study of the times 

 at which these fibres become myelinated is full of interest ; in the first place the fibres to 

 the auditory area become medullated later than those from the external geniculate bodies 

 destined for the visual area; secondly Flechsig has proved that the fibres from the middle 

 geniculate body proceed to the anterior transverse temporal gyrus, and as they become medul- 

 lated before the fibres from the posterior quadrigeminal bodies, he believes that the same 

 gyrus represents the cortical end-station of the cochlear nerve. 



As to the exact limits of the cortical area to which these fibres traceable by embryological 

 methods pass, Flechsig describes the field as consisting of the two transverse temporal gyri, 

 particularly the anterior, and that division of the first temporal gyrus immediately adjacent, 

 that is to say, the third and fourth fifths reckoned from its anterior extremity ; and on 

 inspecting his diagram, Tafel IV, Figur 7 (Gehim und Seele), it is extremely satisfactory 

 to find that the auditory area there figured agrees remarkably with that which I have 

 defined on other lines. 



The work on secondary degenerations by von Monakow, Ferrier and Turner, and Dejerine 

 might be urged in favour of these findings. 



