170 



THE FROG 



CHAP. 



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 peripheral end — be 

 stimulated, there is no result. On the other hand, if the 

 ventral root be cut and its distal end stimulated, 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. y . dorsal root ; g. ganglion of dorsal root ; ^. c. cell in ganglion of dorsal root ; 

 g. fn. grey matter ; M. muscle \ m. c. cell in medulla oblongata ; m.y. motor 

 fibre ; S. skin ; s.f. sensory fibre ; sp. c. spinal cord ; v. c. cells in ventral horn 

 of grey matter ; v. r. ventral root ; w. 7H. white matter. The arrows indicate 

 the direction of the impulses. 



muscles supplied by it will contract, while stimulation of the 

 proximal end produces no result. 



Very accurate observations have shown that the connec- 

 tion 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 {p.r) into the white matter ; and 

 then, its medullary sheath being lost, passes into the ventral 

 horn of the grey matter, its neuraxis being directly con- 



