CHAPTER IV. 



THE CHARACTERISTIC MOTOR FUNCTIONS OF THE NERVE CELLS 

 BELONGING TO THE MID-BRAIN OR PROSOMATIC OUTFLOW OF 

 CONNECTOR NERVES. 



THE final outflow of connector nerves to be considered is that 

 in the prosomatic group of segmental cranial nerves. 



This prosomatic group, which is comparable with the nerves 

 of the segments of the prosoma in such an animal as Limulus, 

 includes the 3rd, 4th and 5th cranial nerves, and just as my 

 anatomical researches in 1885 demonstrated an outflow of fine 

 medullated fibres in the mesosomatic group of nerves, so also 

 I found masses of small medullated fibres in certain roots of 

 the prosomatic group of nerves. These were especially visible 

 in the roots of the 3rd nerve, and following them out along 

 the nerve I found they left it to enter into the ciliary ganglion 

 (Fig. 6). A series of sections through the ciliary ganglion showed 

 that no large medullated fibres, such as are characteristic of the 

 sensory fibres of the fifth nerve, were in connexion with the 

 cells of this ganglion ; any such fibres could be traced through the 

 ganglion without connecting with any of the nerve cells. It was 

 then quite certain that this ganglion was not of the nature of a 

 posterior root ganglion, as had often been asserted by compara- 

 tive anatomists. From this ganglion the short ciliary nerves 

 proceed to supply the sphincter muscle of the iris and the ciliary 

 muscles with motor fibres ; these observations made it certain 

 that the cells in the ciliary ganglion were motor cells to these 

 involuntary muscles of the eye. This conclusion was sub- 

 sequently confirmed by Langley and Anderson by the use of 

 nicotine and the method of degeneration. 



I noticed at the same time a striking peculiarity of the motor 

 fibres from this ganglion, for they were all medullated, not non- 

 medullated as is usual in the motor fibres from the sympathetic 

 nerve cells. We have then here, in the ciliary ganglion, a 



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