478 HANDBOOK OF PHYSIOLOGY. 



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

 with the groups of multipolar cells in the anterior cornua. 1. The in- 

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

 anterior cornu of the same side; but some fibres pass over, through an- 

 terior commissure to end in the anterior cornu of opposite side, proba- 

 bly in 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 backwards to posterior cornu, having no connection with cells. 3. 

 The external fibres are partly in connection with the lateral group of 

 cells in the anterior cornu, but some fibres proceed direct into the lateral 

 column without connection with cells, and pass upwards in it. 



(b) The Posterior roots enter the posterior cornua in two chief bun- 

 dles, either at the tip, through or round the substantia gelatinosa, or by 

 the inner side. The former enter the gray matter at once, and as a 

 rule, turn upwards or downwards for a certain distance and then pass 

 horizontally; some fibres reach the anterior cornua, passing at once 



\r-oot P.M.C. 



FIG. 333. Diagram of the spinal cord at the lower cervical region to show the track of fibres; 

 d. p. ., direct pyramidal tract; L. p. T., crossed pyramidal tract; D. c. T., direct cerebellar tract; 

 p. M. c., posterior median column. A. G. F., anterior ground fibres; A. c., anterior commissure; 

 P. c., post commissure; A. L. A. T., antero-lateral ascending tract; Ant. C., anterior cornu; P. Cor., 

 posterior cornu; c. c. p., intermediate gray substance; L. L. L., lateral limiting layer. (After Gow- 

 ers.) 



horizontally; and the others, the opposite side, through the posterior 

 gray commissure. Of those which enter by the inner side of the cornua 

 the majority pass up (or down) in the white substance of the posterior 

 columns, and enter the gray matter at various heights at the base of the 

 posterior cornu; perhaps some pass directly upwards and inwards in the 

 posterior median column without entering the gray matter. Those 

 that enter the gray matter pass in various directions, some to join the 

 lateral cells in the anterior cornu, some join the cells in the posterior 

 vesicular column, and some pass across to the other side of the cord in 

 the anterior commissure, whilst others become again longitudinal in the 

 gray matter. 



It should be here mentioned that the cells in the posterior vesicular 

 column are connected with medullated fibres which pass horizontally to 

 the white matter of the lateral columns, and there become longitudinal. 



