670 THE NERVOUS SYSTEM 



Functions of the Autonomic Nerves. The Thoracicolumbar Autonom- 

 ies. As we have already seen, the thoracicolumbar fibers have their spinal 

 origin from the first thoracic to the fourth lumbar spinal segments. Yet 

 these fibers are distributed to all portions of the body. They accomplish 

 the following functions : vasomotors to the blood vessels of the entire body ; 

 vasodilators to the blood vessels of the body exclusive of the portions of the 

 skin of the head; the salivary gland, gastric and pancreatic glands and 

 urogenital system; they furnish motor nerves to the heart and inhibitory 

 nerves to the bronchi, stomach and intestine, and both motor and inhibi- 

 tory nerves to portions of the urogenital system; secretory nerves for the 

 sweat glands throughout the body; and the pilomotor nerves of the skin. 

 The details of functional control of these divisions of the thoracic auto- 

 nomies have been discussed in presenting the physiology of the organs 

 concerned. 



The Third Cranial Nerve. Langley has divided the cranial autonomies 

 into the mid-brain autonomies the third cranial nerves, and the bulbar 

 autonomies the seventh, ninth, tenth and eleventh cranial nerves. 



The oculomotor or third cranial nerve is an efferent nerve distributed 

 to the extraocular muscles and to the muscles of the iris and ciliary appara- 

 tus. The fibers to the extraocular muscles are of the usual skeletal motor 

 type. The fibers of the second group belong to the autonomic system. 

 These nerves run by way of the ciliary ganglia where they have their pre- 

 postganglionic synapses. They are distributed to the circular muscles of 

 the eyes which on stimulation cause constriction of the pupils, and to the 

 two sets of muscles in the ciliary apparatus which on stimulation lead to 

 the act of accommodation. 



The Seventh Cranial Nerve. The intermediate nerve of Wrisberg con- 

 tains the autonomic fibers of the facial, figure 413. Fibers of this group 

 constitute the chorda tympani whose function was discovered by Bernard 

 when he demonstrated the presence of secretory fibers to the submaxillary 

 gland. He also proved the presence of vasodilator nerves through this 

 same channel. The chorda tympani stands today as the typical example 

 of a vasodilator and secretory nerve, both functions of the involuntary or 

 autonomic motor type. The cell bodies of the postganglionic neurones 

 lie in the ganglia at the hilus of the gland. The seventh apparently also 

 distributes preganglionic fibers to the spheno-palatine ganglion from 

 whence postganglionic fibers are distributed to the mucous membrane of 

 the nose and upper respiratory passages. 



The Ninth Cranial Nerve. The tympanic branch of the ninth cranial 

 nerve supplies vasodilator and secretory fibers to the parotid gland. 



