CHAP, ii.] THE BRAIN. 949 



Concerning the course taken by the other less conspicuous 

 " descending " tract, the antero-lateral descending tract, our know- 

 ledge is very imperfect ; nothing definite can be said at present. 



The cerebellar tract, occupying near to the surface a position 

 which in the series of sections (Fig. 109, Gb) appears now rather 

 more ventral now more dorsal, eventually passes into the restiform 

 body, of which it forms a large part, and thus reaches the cere- 

 bellum. The antero-lateral ascending tract possibly also takes the 

 same course, but this is not as yet certain. 



The median posterior tract or column, becoming the fasciculus 

 gracilis, ends in the gracile nucleus; and in a similar manner 

 the external posterior column, or fasciculus cuneatus, ends in the 

 median and lateral masses of the cuneate nucleus. As we have 

 seen, the white matter of these columns diminishes as the nuclei 

 increase ; and the nuclei after absorbing, so to speak, the white 

 matter diminish in turn ; the ascending degeneration observed in 

 these columns stops at these nuclei. It is a suggestive fact that 

 as these nuclei diminish forwards the restiform body increases in 

 bulk. 



The remaining fibres of the cord, belonging partly to the 

 anterior column and partly to the lateral column, not gathered 

 into any of the above mentioned tracts, appear to end chiefly at 

 all events in the reticular formation of the bulb itself, though 

 some are carried on to the higher parts of the brain. 



612. Thus of the various tracts or strands of the spinal cord 

 two only are known definitely and certainly to pass as conspicuous 

 unbroken strands through the bulb to or from higher parts; 

 namely, the pyramidal tract to the cerebrum and the cerebellar 

 tract to the cerebellum. All or nearly all the rest of the longitu- 

 dinal fibres of the cord reaching the bulb end, as far as we know 

 at present, in some part or other of the bulb ; and we may infer 

 that some or other nerve cells of the bulb serve as relays to 

 connect these fibres of the cord with other parts of the brain. 



The gracile and cuneate nuclei stand out conspicuously as 

 relays of this kind, and through them the posterior columns of 

 the cord make secondary connections on the one hand with the 

 cerebellum and on the other hand with various regions of the 

 cerebrum. We have said 606 that fibres passing ventrally from 

 the gracile and cuneate nuclei sweep in a curved course through 

 the reticular formation as the internal arcuate fibres (Fig. 109, 

 /. a. i.). The hindmost of these form the superior decussation 

 already referred to as seen in sections at the fore-part of and in 

 front of the pyramidal decussation (Fig. 109, 3, supra Py. dec.}. 

 After decussating ventral to the central canal these fibres form an 

 area called the inter-olivary layer (Fig. 109, 4, in. ol.) lying dorsal 

 to the pyramids between the two olivary nuclei. This layer may 

 be regarded as the hind end or beginning on each side of a remark- 

 able longitudinal strand called the fillet (Figs. 108, B.F., 110, F.) y 



