HISTORY OF THE INVOLUNTARY NERVOUS SYSTEM ^ 



FIG. i. THE REFLEX PATHS oV THE VOLUNTARY SYSTEM IN THE 



CRANIAL REGION. 



The afferent receptor neurons are shown in blue, the connector neurons in 

 black, the efferent excitor neurons in red. This scheme of colouring holds for all 

 the figures in this book. 



The splanchnic excitor neurons are shown in the lower part of the diagram ; 

 the somatic excitor neurons in the upper part. The receptor neurons for both 

 systems all run in the fifth and tenth nerves which are shown in the lower part of 

 the diagram. 



The neurons in a vertical line all belong to the same segment, the first six lie 

 in the prosomatic segments, and the remainder in the mesosomatic. 



The receptor fibres of the somatic system all run in the fifth nerve, their nuclei 

 lying in the gasserian ganglion, G.G. 



The ascending sensory root, A.S.V., supplies the connector neurons of the 

 prosomatic segments of the somatic system. These connector neurons, which lie 

 close against the ascending root, communicate with the excitor neurons of the four 

 segments comprising the nucleus of the third nerve, with the nucleus of the fourth 

 nerve, and with the anterior portion of the nucleus of the sixth nerve in the respec- 

 tive segments. The descending sensory root, D.S.V., communicates with the con- 

 nector neurons of the mesosomatic segments of the somatic system. The connector 

 neurons connect in the first mesosomatic segment with the more posterior portion 

 of the excitor nucleus of the sixth nerve and the others with the series of nuclei 

 which form the excitor nucleus of the twelfth nerve. 



The receptor fibres of the splanchnic system in the prosomatic region all run in 

 the fifth nerve. They form part of the ascending sensory root and connect in each 

 segment with connector neurons which in their turn connect with the nuclei of the 

 descending motor root of the nerve, D.M.V. The nuclei of the two posterior seg- 

 ments form the nucleus masticatorius, N.M. Some afferent fibres of the fifth nerve 

 probably connect also with the connector neurons of the seventh nerve as shown in 

 the diagram. 



The afferent fibres of the mesosomatic segments of the splanchnic system all 

 run in the sensory portion of the tenth nerve, their cells lying in the vagus gan- 

 glion, V.G. 



A small ascending root connects with the connector neurons of the first three 

 segments; the connector neurons in their turn connect with the motor nuclei, the 

 first two of which give origin to the seventh nerve and the third to the ninth nerve. 



The descending root, the fasciculus solitarius, F.S., connects with the connector 

 neurons of the remaining segments which lie in the dorsal nucleus of the vagus, 

 D.N.X. The motor neurons of these segments form the motor portion of the tenth 

 nerve, the segmental nuclei lying in the nucleus ambiguus, N.A. 



