470 



COMPARATIVE PHYSIOLOGY. 



B 



Secondary degeneration ensues in these tracts upon certain 



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. Simi- 

 larly to the first, degenera- 

 tion follows in these tracts 

 when there are brain. - le- 

 sions of the motor area. 

 Hence, both of these consti- 

 tute descendingmotor 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 lateral column. 



5. Mixed Lateral Coir 

 umns. — These and the pre- 



V 

 C 



V 

 D 



FiQ. 335.— Diagrammatic representation of col- 

 umns and conducting paths in spinal cord ceding are functionally sim- 



in upper dorsal region (after Flint and ., , „ -,. ... _ , 



Landois). AR. AE, anterior roots of spi- liar tO 3. JN either 3, 4, nor 



5 degenerate, on section of 

 the cord, from which it is 

 inferred that they have 



spi- 

 nal nerves; PR, PE, posterior roots; A, 

 columns of Tnrck (antero - median col- 

 umns) ; B, anterior fundamental fascicu- 

 lus; C, columns of GoU; D, columns of 

 Burdach; E, B, anterior radicular zones; 



F, F, mixed lateral columns; G, G, crossed , . n i ji i i 



pyramidal tracts; H, H, direct cerebellar trophlC cells both above and 

 fibers. 1 1 



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 

 cells are to be referred to the posterior gray cornua of the cord, 

 which they connect in all probability with the cerebellum. 



7. Columns of Burdach (postero-lateral columns). — This 

 tract is connected with the restiform bodies and reaches the 

 cerebellum by the inferior peduncles. Secondary degenera- 

 tions do not occur in these fasciculi, so that it seems likely that 

 they connect nerve-cells at different levels in the cord; and 



