DEVELOPMENT OF PERIPHERAL NERVOUS SYSTEM 837 



vation to the iris of the eye occurs through the thoracicolumbar autonomic 

 system as follows: 



Cell bodies of preganglionic neurons in intermedio-lateral column of spinal 

 cord, from which preganglionic fibers pass to superior cervical ganglion of 

 autonomic nervous system. Cell bodies of postganglionic fibers lie in the su- 

 perior cervical ganglion and fibers pass from this ganglion along the internal 

 carotid plexus to the ophthalmic division of the fifth nerve, and from thence 

 along the long ciliary and nasociliary nerves to iris. Function: dilation of the 

 pupil. 



2) Autonomic Efferent Innervation of the Heart. Preganglionic cell bodies 

 in dorsal motor nucleus of vagus in myelencephalon. Fibers pass by way of 

 vagus nerve to terminal (intrinsic) ganglia of the heart. Postganglionic cell 

 bodies in terminal ganglia of heart; postganglionic fibers pass to heart muscle. 

 Function: slows the heart beat. The foregoing represents the craniosacral au- 

 tonomic or parasympathetic innervation. The corresponding sympathetic in- 

 nervation is as follows: 



Preganglionic cell bodies in intermedio-lateral column of spinal cord; pre- 

 ganglionic fibers pass to superior, middle and inferior cervical ganglia of sym- 

 pathetic ganglion series. Postganglionic cell bodies in cervical ganglia from 

 which postganglionic fibers pass via cardiac nerves to cardiac musculature. 

 Function: acceleration of heart beat. 



d. Ganglia of the Autonomic System and Their Origin 



The ganglia of the autonomic nervous system represent aggregations of the 

 cell bodies of postganglionic neurons; the cell bodies of the preganglionic 

 neurons lie always within the central nervous system. These autonomic ganglia 

 arise from two sources; viz.: 



1 ) The neural crest material of the dorsal root ganglion of the spinal nerves 

 and the neural crest material associated with certain cranial nerves, and 



2) from cells of the neural tube which migrate from the tube along the 

 forming ventral or efferent nerve roots of the spinal nerves (Kuntz and 

 Batson, '20). 



These migrating neural cells become aggregated to form three sets of ganglia 

 as follows: 



1 ) The sympathetic chain ganglia lying on either side of the vertebral 

 column. 



2) The collateral or subvertebral ganglia located between the chain ganglia 

 and the viscera. Examples of collateral ganglia are the coeliac, superior 

 mesenteric and inferior mesenteric ganglia. 



3 ) The terminal or intrinsic ganglia lie near or within the organ tissue such 

 as the ciliary and submaxillary ganglia. 



