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HANDBOOK OF PHYSIOLOGY. 



and converging bundles from the anterior column of the cord; the pos- 

 terior root by more numerous parallel bundles, from the posterior column, 

 or, rather, from the posterior part of the lateral column (fig. 350), for 

 if a fissure be directed inward from the groove between the middle and 

 posterior columns, the posterior roots will remain attached to the former. 

 The anterior roots of each spinal nerve consist chiefly of efferent fibres; 

 the posterior exclusively of afferent fibres. 



Course of the Fibres of the Spinal Serve- Roots. (a) The Anterior 

 roots enter the cord in several bundles, which may be called :(!) 

 Internal; (2) Middle; (3) External; all being more or less connected with 

 the groups of multipolar cells in the anterior cornua. 1. The internal 

 fibres are partly connected with internal group of nerve-cells of the 



Fig. 352A. Section of the spinal cord, showing the arrangement of the white and gray matter. 

 1, Direct pyramidal tract; 2, 3, antero-lateral column; 4, ascending lateral column; 5, crossed 

 pyramidal tract; 6, direct cerebral tract; 7, column of Burdach; 8. column of Goll; 7, posterior 

 median fissure; 10. anterior median fissure; 11, 18. anterior horn cells; 13, Clarke's column ; L. R., 

 Lissauer's column ; r p, posterior root ; r a, anterior root. 



anterior cornu of the same side; but some fibres send collaterals through 

 the anterior commissure to end in the anterior cornu of opposite side, 

 probably in the internal group of cells. 2. The middle fibres are partly 

 in connection with the lateral group of cells in anterior cornu, and in 

 part pass backward to the posterior cornu, having no immediate connec- 

 tion with cells. 3. The external fibres are partly in connection with the 

 lateral group of cells in the anterior coruu, but some fibres proceed di- 

 rect into the lateral column without connection with cells, and pass 

 upward in it. 



Besides these fibres, there are some which do not appear to have any 

 connection with the anterior horn cells, but pass directly through to 



