CHAPTER III. 



THE CHARACTERISTIC MOTOR FUNCTIONS OF THE NERVE CELLS 

 BELONGING TO THE BULBO-SACRAL OUTFLOW OF CON- 

 NECTOR NERVES. 



THE motor nerve cells, which supply motor fibres to involuntary 

 muscles associated with the cranial nerves,, fall into two distinct 

 groups in accordance with the natural division of these nerves 

 into a foremost or prosomatic and a hindmost or mesosomatic 

 group. In each of these groups motor nerve cells to involuntary 

 muscle are found situated outside the central nervous system, 

 those in the ciliary ganglion belonging to the prosomatic region 

 and those in connexion with the bulbar group of nerves to the 

 mesomatic region. In this chapter I propose to deal with the 

 latter group and to consider their functions at the same time as 

 those of the motor nerve cells of the sacral outflow on account of 

 the close functional relationship of these two outflows. 



In the sacral outflow there are undoubtedly motor nerve 

 cells which are not situated in the central nervous system, but 

 connect with it by means of the pelvic nerve. The position of 

 the motor neurons and their connexion with the central nervous 

 system by means of the vagus and pelvic nerves respectively re- 

 semble so closely the arrangement of the sympathetic motor 

 neurons, as to make it almost certain that these communicating 

 fibres in the vagus and pelvic nerves must both be regarded as 

 connector fibres to motor neurons. The embryological evidence 

 that the latter have travelled out from the central nervous 

 system to the periphery has already been mentioned in chapter I. 

 and will be given more fully in chapter vm. 



In all mammals without exception contraction of the unstriped 

 muscles of the small intestine takes place upon stimulation of the 

 vagus nerve, and Bayliss and Starling have proved, by means 

 of the enterograph, that both longitudinal and circular muscles 

 contract when the vagus is stimulated, and that neither contract 



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