170 



THE FROG 



CHAP. 



passing into the cord by the dorsal root, the motor 

 by the ventral root. As a consequence of this, if the 

 dorsal root be cut and its proximal or central end 

 i.e., the end in connection with the cord stimulated, 

 muscular contraction will follow just as if the stimulus 

 had been applied to the skin supplied by the nerve 

 in question. If the other cut end the distal or peri- 

 pheral end be stimulated, there is no result. On the 



FIG. 55. Diagram illustrating the paths taken by the nervous impulses. 

 c. c. central canal ; col. collaterals ; c. cort. cell in rind or cortex of the cerebral 

 hemisphere ; c, g. smaller cerebral cell ; d. c. cells in dorsal horn of grey matter ; 

 d. r. dorsal root ; g. ganglion of dorsal root ; g. c. cell in ganglion of dorsal root ; 

 g. m. grey matter ; M. muscle ; m. c. cell in medulla oblongata : i. f. motor 

 fibre ; S. skin ; s. /. sensory fibre ; sp. c. spinal cord : i'. c. cells in ventral horn 

 of grey matter; v. r. ventral root; w. m. white matter. The arrows indicate 

 the direction of the impulses. 



other hand, if the ventral root be cut and its distal 

 end stimulated, the muscles supplied by it will contract, 

 while stimulation of the proximal end produces no 

 result. 



Very accurate observations have shown that the con- 

 nection between the motor and sensory fibres is as 

 follows (Fig. 55). A motor fibre (m. f) is traceable 

 from the nerve-trunk through the ventral root (u. r) 

 into the white matter ; and then, its medullary sheath 



