488 ANIMAL PHYSIOLOGY. 
the brain, that a conducting path in the nervous centers is not 
synonymous with conducting fibers. The cells themselves and 
the neuroglia probably are also 
AN conductors. We shall now en- 
deavor to map out, as estab- 
lished by the method of Flech- 
sig, Waller, and others, the 
main fiber tracts of the spinal 
cord, 
1. Antero-median Columns 
-(columns of. Tirck). These 
probably decussate in the cerv- 
cial region, where they are most 
marked, constituting the direct 
or uncrossed pyramidal tract, 
and disappear in the lower dor- 
sal region. 
~ 
Fia, 346.—Diagrammatic representation of 
columns and conducting paths in spinal 
eord in ypper dorsal region (after Flint 
and Landois). AR, AR, anterior roots of 
spinal nerves ; PR, PR, posterior roots ; 
A, columns of Tiirck (antero-median col- 
umns); B, anterior fundamental fascic- 
ulus ; C, columns of Goll; D, columns of 
. Burdach ; E, E, anterior radicular zones ; 
F, F, mixed lateral columns; G, G, 
crossed pyramidal tracts ;-H, H, direct 
~ cerebellar fibers. 
Secondary degeneration en- 
sues in these tracts upon cer- 
tain brain-lesions, in the motor 
regions, 
2. Crossed Pyramidal Tracts. 
—They pass forward to form 
part of the anterior pyramids of 
the medulla after decussation 
in their lower part. Similarly to the first, degeneration follows 
in these tracts when there are brain-lesions of the motor area. 
Hence, both of these constitute descending motor paths. 
3. Anterior Fasciculi (fundamental or ground bundle).— 
They possibly connect the gray matter of the cord with that of 
the medulla. 
4, Anterior Radicular Zones, in the anterior part of the lat- 
eral column. 
5. Mixed Lateral Columns.—These and the preceding are 
functionally similar to 3. Neither 3, 4, nor 5 degenerate, on 
section of the cord, from which it is inferred that they have 
trophic cells both above and below. 
6. Direct Cerebellar Tracts——These bundles, passing by the 
funiculi graciles or posterior pyramids of the medulla, reach 
the cerebellum by its inferior peduncles. 
These fasciculi enlarge from their site of origin in the lum- 
bar cord upward. After section of the cord they show ascend- 
ing degeneration, so that it seems probable that their trophic 
