184 LECTURES ON THE CENTRAL NERVOUS SYSTEM. 



lie in a thick stratum dorsad of the pyramids, which have, at 

 this level, completed their decussation. The region in which 

 they lie is the one which was occupied hy the antero-lateral 

 columns in the spinal cord. The main mass of crossed sensory 

 tracts which ascended in the latter is crowded backward and 

 outward by these new-comers. Thus, the now united crossed 

 sensory tract fills up all the space between the olivary bodies 

 (olivre inferiores). The latter are gray masses, which first appear 

 in the medulla oblongata at this level. The higher we pass in 

 the medulla oblongata, the fewer fibres are there found in the 

 posterior columns. Gradually, nil of them pass, by way of the 

 arciform fibres, to the decussation of the lemniscus, and extend to 

 the opposite side near the middle line, where they form the inter- 

 olivary layer, or, as we will call it from now on, the layer of the 

 fillet. The fibres of this layer pass to the fillet of the mid-brain. 



It has been frequently claimed that the fibres of the pos- 

 terior columns do not follow this course, but rather pass into the 

 olivary bodies, and from there through the posterior peduncles 

 of the cerebellum into that body. My investigations have 

 shown, however, that they all, or nearly all, follow the course I 

 have described. At the embryological period of which I was 

 speaking, both -the olivary bodies and their whole vicinity are 

 destitute of medullary fibres. We can therefore prove, in the 

 most convincing manner, that the fibres of the posterior columns 

 have no connection whatever with them, but only pass through 

 them. Fig. 110 represents a section through the same foetal 

 oblongata shown in Fig. 109. This section is made somewhat 

 higher up than the latter, and shows clearly the point of which 

 I speak. You see that the fibres pass through the olivary 

 bodies (which at this level have the appearance of plicated 

 medullary laminae) to the decussation in the middle line (raplie, 

 continuation of the decussation of the fillet). 



Fig. Ill is a diagram of the course of the sensory fibres. 

 Let us, with the aid of this diagram, trace out the course of the 

 separate tracts, and ascertain what location in the medulla is 



