igo 



SCIENCE PROGRESS. 



of view how section i across a fibre/;)/ causes degeneration 

 below but not above, than upon the older view that the 

 fibre py is in continuity at both ends with a cerebral and a 

 spinal nerve-cell. 



But the full possible significance of the nerve-valve 

 conception as regards direction of Wallerian degeneration 

 and direction of nerve-impulses comes out better on exami- 

 nation of the following diagram and table, which, besides 

 this best-known case of the efferent tract, gives all the less 

 well-known cases that present themselves in the afferent 

 tract as w T ell : — 



iv o—4 



V Brain Cells 



./( y VT Bulb and Cord- ceils 



SensiJicafory end - oryarv 



^fotor end,- organ 



I. Sensificatory end-organ. 

 II. Ganglion cell of posterior root. 



III. Spinal cell of Clarke's column, and of Burdach's bulbar nuclei. 



IV. " Sensory" brain cell, cerebral and cerebellar. 

 V. " Motor " brain cell. 



VI. Spinal cell, bulbar nuclei and anterior cornu. 



I. III. IV. afferent tract. V. VI. VII. efferent tract. 



From I. to III. periphery to medulla ; afferent nerve-fibres. 



From III. to IV. medulla to cortex; Goll's column; cerebellar tracts; 



crura cerebri. 

 From V. to VI. cortex to medulla ; pyramidal tracts. 

 From VI. to VII. medulla to periphery ; efferent nerve-fibres. 



III. to IV. spinal communication. 



IV. to V. cerebral communication. 



Impulses can pass from I. to III., Ill to IV., V. to VI., VI. to VII., also from III. 

 to VI., IV to V. 



Impulses cannot pass from VII. to VI., VI. to V., IV. to III., III. to I., nor 

 from VI. to III., V. to IV. 



The above schema of the physiological anatomy of the 

 nervous circuit is intended to embodv the best attested facts 



