THE AUTONOMIC NERVOUS SYSTEM 387 



of connector fibres runs out in the glossopharyngeal nerve 

 through the lesser superficial petrosal nerve to the otic 

 ganglion, from which exciter neurons innervate the parotid 

 salivary glands. 



A very interesting feature of the connector fibres of the 

 parasympathetic autonomic nervous system is, that while 

 those of the oculomotor (midbrain outflow) and of the sacral 

 outflow connect with the central nervous system through 

 ventral nerve- roots, those of the facial, glossopharyngeal, and 

 vagus (hindbrain outflow) run in dorsal nerve-roots. 



The anatomy of the autonomic system in the head is 

 slightly complicated. The anterior prolongation of the lateral 

 sympathetic chain of the trunk continues forwards, accompany- 

 ing the internal carotid artery as the internal carotid nerve. A 

 branch of it (the deep petrosal) joins the palatine nerve (forming 

 the Vidian nerve) and runs to the spheno-palatine ganglion. 

 This ganglion is also connected to the maxillary branch of the 

 trigeminal. Another sympathetic branch runs to the ciliary 

 ganglion, which is also connected to the ophthalmic branch of 

 the trigeminal. The sympathetic exciter neurons from the 

 anterior cervical ganglion are thus able to make their way into 

 the eye to the iris-muscles. The mandibular branch of the 

 trigeminal connects with the chorda tympani and the sub- 

 maxillary ganglion. 



Further mention must be made of Auerbach's plexus, 

 which lies between the circular and longitudinal coats of 

 muscles on the intestine. The neurons which compose it 

 are the exciters of the parasympathetic outflow through the 

 vagus, and these neurons branch, the two axon fibres having 

 different destinations. A mass of food in the intestine stimu- 

 lates the muscles above it to contract, and those below it to 

 slacken, thus causing peristaltic action. This is particularly 

 interesting because peristalsis can occur when all the nerves 

 to the intestine are cut, which means that local reflex arcs are 

 formed in Auerbach's plexus. Another plexus (Meissner's), 

 which lies within the muscle-coats of the intestine, has an 

 unknown function. 



The effect of impulses travelling out through the para- 



