THE WHITE MATTER OF THE SPINAL MEDULLA. 537 



:isciculi which pass upwards in the spinal medulla to reach the medulla 

 blongata, the pons and cerebellum, the mesencephalon (corpora quadrigemina), 

 rie thalanius, and the cerebral hemisphere. In the neighbourhood of each level 

 here these ascending sensory tracts end, such as for example the region of the 

 estibular nucleus and cerebellum, the tectum mesencephali, the corpus striatum, 

 nd the cerebral hemisphere, great descending tracts originate and pass downwards 

 i the spinal medulla (Fig. 475 the red lines). Thus we have cerebro-spinal, 

 ubro-spinal, tecto-spinal, vestibulo-spinal, and bulbo-spinal fasciculi passing down 

 he spinal medulla ; and each system eventually ends around the series of motor 

 .uclei (Fig. 475), many of them in the spinal medulla. 



In the anterolateral funiculus the various fasciculi will be found to be 

 rouped roughly into three bands : Next to the gray columns is the fasciculus 

 >roprius ; then comes a band of descending (motor) fasciculi ; and then, upon the 

 urface, a series of ascending (sensory) fasciculi. This arrangement, however, is not 

 naintained with any degree of exactitude in the anterior funiculus, where the 

 harp demarcation between ascending and descending fasciculi is in great part 

 lestroyed by the intermingling of fibres passing in opposite directions. 



The fibres of the posterior nerve-root have already been studied so far as their 

 elation to the posterior funiculus is concerned. No clear conception of the nature 

 ind significance of the ascending fasciculi in the anterolateral funiculus can be ob- 

 ,ained unless they also are studied in relationship with the fibres of the posterior root. 



It has already been explained that of the fibres which enter the spinal 

 nedulla in the posterior root the great majority enter the posterior funiculus, 

 .vhere they bifurcate (Fig. 473, a) ; one branch of each fibre passes upwards either 

 n the funiculus gracilis or in the funiculus cuneatus, or it may pass from the 

 Latter into the former ; the other descends in the fasciculus interfascicularis (O.T. 

 3omma tract). Other fibres perhaps enter the posterolateral fasciculus (O.T. 

 Lissauer's bundle). But all the other fibres of the posterior root, together with 

 the majority of the fibres of the fasciculus cuneatus, sooner or later enter the gray 

 matter (Fig. 473, ~b to Ji) of the spinal medulla. 



Some of them (&) pass directly to end in the nucleus dorsalis of their own side, 

 and from its cells fresh fibres arise, which pass laterally through the posterior 

 column and lateral funiculus to reach the surface, where they bend upwards as 

 constituent fibres of the spino-cerebellar fasciculus. These pass upwards throughout 

 the whole length of the spinal medulla (above their place of origin), into the 

 medulla oblongata, thence into the cerebellum through the restiform body. 



Other fibres on the same side (e), and perhaps also on the other side (d), end 

 | amidst cells of the gray matter, the axis-cylinder processes of which' pass into the 

 antero-lateral superficial fasciculus (O.T. Gowers' tract). In this tract they ascend 

 throughout the spinal medulla, medulla oblongata, and pons, to enter the cere- 

 bellum alongside the brachium conjunctivum (superior peduncle). This element 

 in the antero-lateral fasciculus is sometimes designated the fasciculus spinocere- 

 bellaris anterior, to distinguish it both from the non-cerebellar fibres of the parent 

 fasciculus and from the fasciculus spinocerebellaris [posterior] (O.T. the direct cere- 

 bellar tract). These two spino-cerebellar tracts convey to the cerebellum informa- 

 tion from the muscles and overlying skin which assists it to co-ordinate the 

 muscles for carrying on precisely adjusted movements. 



Other fibres of the posterior nerve-root (e,f, g, and A) terminate in relation- 

 ship with cells in the gray columns of their own side of the spinal medulla, the 

 axons of which cross the median plane in the anterior commissure to pass respectively 

 j () into the anterolateral superficial fasciculus [not to be confused with the 

 cerebellar constituents of this bundle] ; (/) into the real fasciculus spinothalamicus 

 [posterior], of which the last-mentioned fibres are merely outlying members; 

 ( (g) into the fasciculus spinotectalis, to ascend to the mesencephalon ; and (h) into 

 the marginal area of the anterior funiculus to form a group which may be called 

 the fasciculus spinothalamicus anterior. 



The careful investigations of the late Dr. Page May led him to attach a definite 

 physiological significance to this grouping of the ascending paths. The fasciculus 

 spinothalamicus [posterior] is supposed to convey upwards to the thalamus (for 



