COMPONENT PARTS OF WHITE MATTER OF SPINAL CORD. 433 
fibres entering from the series of posterior nerve-roots is not nearly so complete as in 
the case of the monkey. 
Numerous collateral fibrils stream into the gray matter of the posterior horn both 
from the ascending and descending branches of the entering fibres of the posterior nerve- 
roots. These are classified into long and short collaterals. The long collaterals extend 
forward into the anterior horn of gray matter and end in relation to the ventral nerve- 
cells. The short collaterals end in relation to the nerve-cells in the substantia Rolandi, 
the nerve-cells of Clarke’s column, and the other nerve-cells of the posterior horn (Fig. 
320, p. 426). 
Tract of Lissauer.—This is a small tract of nerve-fibres of minute calibre which 
assume their medullary sheaths at a comparatively late period. It is placed at the 
surface of the cord close to the postero-lateral furrow. It is formed by some of the 
outer fibres of the posterior nerve-roots, which do not enter the tract of Burdach, and 
which pass upwards in the cord close to the substantia gelatinosa Rolandi, in which they 
ultimately end. 
Association Fibres in the Posterior Column.—But the whole of the fibres of the 
posterior column are not derived from the posterior nerve-roots. A few fibres exist in 
this column which have a different origin. In all probability they are derived from some 
of the cells of the gray matter of the cord, and pass upwards or downwards in the 
posterior column for a varying distance before they finally turn in to end in the gray 
matter at a higher or a lower level. These fibres, therefore, constitute links of con- 
nexion between different cord segments, and thus they are termed association or longi- 
tudinal commissural fibres. Our information regarding these fibres at present is some- 
what defective ; but it may be mentioned that it is probable that the “comma” tract of 
Schultze, in the deeper part of the posterior column, and the descending septo-marginal 
tract of Bruce, placed nearer the surface, belong mainly to this category. 
Lateral Column of the Cord.—In the lateral column of the cord the well- 
established tracts are: 
1. The direct cerebellar tract. 
2. The tract of Gowers. 
3. The crossed pyramidal tract. 
The remainder of the column goes under the name of the lateral basis-bundle. 
The direct cerebellar tract (fasciculus cerebello-spinalis) is a band-like strand 
which hes in relation to 
the surface of the cord 
immediately in front of 
the postero-lateral 
groove. It is an ascend- 
ing tract and is com- 
posed for the most part 
of coarse large nerve- 
fibres, which are de- 
rived from the nerve- 
cells of the posterior 
vesicular column 
(Clarke’s column) in the 
posterior horn of gray 
matter. It is, therefore, 
not found through the 
whole length of the cord. 
It first appears in the 
lower part of the dorsal 
region; and as it ascends 
it gradually increases in Fic. 322.—Dr1aGRaAMMATIC REPRESENTATION OF A TRANSVERSE SECTION 
pize-as it is joined by THROUGH THE SPINAL Corp. 
the axons of the cells of 
Clarke’s column, which 
lie at higher levels. It finally enters the medulla oblongata, and through this 
proceeds to the cerebellum, in which it ends. 
Gowers’s tract (fasciculus antero-lateralis superficialis) lies in front of the direct 
28 
Entering posterior 
ae 
Lissauer’s tract 
ee 
Love $.17109 
OIR.PYR. TRACT. 
DIR.PYR.TRACT 
Emerging anterior root 
The nerve tracts in the white matter and the clusters of nerve-cells 
in the gray matter are shown. 
