MO TOR FUNCTIONS OF THE BULBO-SA CRAL O UTFLO W 63 



former form the motor nerves of involuntary or unstriped muscle. 

 The voluntary motor nerve cells are connected with the connector 

 nerve cells by connector nerve fibres. These connector fibres 

 give off collaterals and so connect the higher centres with a 

 number of voluntary segments. v The involuntary motor nerve 

 cells are likewise connected with higher centres by connector 

 nerves, the fibres of which give off collaterals and so connect the 

 higher nerve centres with a number of involuntary segments. In 

 the latter case these connector nerves are naturally partly within 

 and partly without the central nervous system. Those parts, 

 which run free of the central nervous system to the vagrant motor 

 cells, form part of such nerves as the vagus nerve, the rami com- 

 municantes of the sympathetic system and the pelvic nerve. 

 These connector nerves of the involuntary nervous system have 

 left the central nervous system in three main outflows, a bulbar 

 outflow known as the vagus system, a thoracico-lumbar outflow 

 known as the sympathetic system, and a sacral outflow, the pelvic 

 system. These three outflows are separated from each other by 

 the interpolation of segments belonging to the voluntary system, 

 which are especially developed owing to the formation of the 

 vertebrate limbs. 



The three outflows differ in function in a striking manner. 

 The motor cells of the sympathetic system send motor fibres to 

 the muscles of the heart and of the blood vessels over the 

 whole body, and to a system of involuntary muscles, which pos- 

 sibly arose from a system of dermal muscles situated just under 

 the skin over the whole body. 



The motor cells of the vagus and pelvic systems send motor 

 fibres to a system of involuntary muscles belonging to the 

 alimentary canal and its derivatives, a system of endodermal 

 muscles, the vagus group being confined to the small intestine 

 and its derivatives, and the pelvic group to the large intestine 

 and its derivatives. 



The connector nerve cells whose axons form connector fibres to 

 the motor neurons are all situated in the central nervous system, 

 but, owing to the difference of position of the motor neurons of 

 the involuntary nervous system as compared with those of the 

 voluntary nervous system, the connector nerves of the involuntary 

 nervous system pass out of the central nervous system and thus 

 form the efferent part of such nerves as the vagus and pelvic nerves. 



