THE SYMPATHETIC NERVOUS SYSTEM 339 



and plexuses, to end in relation with involuntary muscle or glandular tissue. 

 A very few postganglionic fibers acquire delicate myelin sheaths. 



Three streams of preganglionic fibers leave the cerebrospinal axis (Fig. 250). 

 The cranial stream includes the general visceral efferent fibers of the oculomotor, 

 facial, glossopharyngeal, vagus, and accessory nerves. These fibers end in the 

 terminal ganglia, already mentioned, which are located close to or within the 

 organ which they innervate. In the cervical nerves there are no visceral ef- 

 ferent fibers, the cranial stream being separated from the next by a rather wide 

 gap. The thoracicolumbar stream includes the fibers which arise from the cells 

 of the intermediolateral column of the spinal cord and make their exit through 

 the thoracic and first four lumbar nerves (Langley, 1892; Miiller, 1909). After 

 leaving the spinal nerves by way of the white rami they enter the sympathetic 

 nervous system and terminate in the ganglia of the sympathetic trunk or in the 

 celiac and associated collateral ganglia (Fig. 250). The sacral stream includes 

 the visceral efferent fibers of the second, third, and fourth sacral nerves. These 

 arise from cells in the lateral column of gray matter in the sacral portion of the 

 spinal cord and run through the visceral branch of the third sacral and a similar 

 branch from either the second or fourth sacral nerves. These fibers end in the 

 ganglia of the pelvic sympathetic plexuses. 



The Autonomic Nervous System. For many reasons it is convenient to have 

 a name which will designate the sum total of all general visceral efferent neurons, 

 both preganglionic and postganglionic, whether associated with the cerebral 

 or spinal nerves. For this purpose the term "autonomic nervous system" is 

 in general use. It designates that functional division of the nervous system 1 

 which supplies the glands, heart, and smooth musculature with their efferent in- I 

 nervation (Fig. 250). It is important to bear in mind that this is a functional 

 and not an anatomic division of the nervous system, that it includes only efferent 

 elements, and that the preganglionic neurons lie in part within the cerebrospinal 

 nervous system. The terminal portions of the preganglionic fibers and the 

 postganglionic neurons are located in the sympathetic system. According to 

 the origin of the preganglionic fibers, we may recognize the following three 

 subdivisions of the autonomic system: (1) the cranial autonomic system, whose 

 preganglionic fibers make their exit by way of the third, seventh, ninth, tenth, 

 and eleventh cranial nerves; (2) the thoracicolumbar autonomic system, whose pre- 

 ganglionic fibers make their exit by way of the thoracic and upper lumbar spinal 

 nerves; and (3) the sacral autonomic system, whose preganglionic fibers run in 

 the visceral rami of the second, third, and fourth sacral nerves (Fig. 250). 



