NEURO-MUSCULAR MECHANISM 155 



(3) The ninth nerve sends fibres to the parotid gland, which 

 have their cell station in the otic ganglion. 



(4) The vagus sends inhibitory fibres to the heart, which 

 form synapses in the cardiac plexus. It also sends motor 

 fibres to the ossophagus and stomach, which, in some animals 

 at least, have the cell stations in the ganglion of the 

 trunk. 



(5) The nervi erigentes come off from the second and third 

 sacral nerves, and pass to the hypogastric plexus near the 

 bladder where the fibres have their cell stations. They are 

 the vaso-dilator nerves to the pelvic organs, inhibit the 

 retractor penis, and are motor to the bladder, colon, and 

 rectum. 



(b) Ingoing Fibres. The course of these from the viscera 

 is not so clearly known ; but they appear to enter the main 

 nerve largely by the white rami. In the normal condition 

 stimulation of their peripheral endings does not lead to 

 modifications of consciousness, and is therefore not accom- 

 panied by pain. But in abnormal conditions painful sensa- 

 tions are produced. In some cases abnormal stimulation 

 of visceral nerves leads to painful sensations referred to 

 the cutaneous distribution of the spinal nerve with which 

 they are connected. Thus, disease of the heart is often 

 accompanied by pain in the distribution of the upper dorsal 

 nerves in the left arm, with which the visceral fibres to 

 the heart are associated. 



