CHAPTER XVII 

 THE VISCERAL AND GUSTATORY APPARATUS 



OUR knowledge of the functional localization within the spinal 

 cord of the general visceral reflex centers related to the spinal 

 nerves is still rather indefinite. Most of the cerebro-spinal 

 control of the visceral reactions of the body is effected from the 

 bulbar sympathetic centers by way of the vagus nerve. The 

 afferent fibers of these systems all enter the fasciculus solitarius, 

 a longitudinal bundle of fibers in the lower part of the medulla 

 oblongata, and they terminate in the nucleus of visceral sensory 

 neurons which accompanies this fasciculus (Figs. 71-74, 77, 

 114). The special visceral fibers of the nerves of taste also ter- 

 minate in this nucleus. The efferent fibers of these systems arise 

 chiefly from the dorsal motor nucleus of the vagus, a cluster of 

 neurons which produces an eminence in the floor of the fourth 

 ventricle known as the ala cinerea or trigonum vagi (Figs. 71- 

 74, 114). From this nucleus arise preganglionic fibers for the 

 innervation of various systems of visceral muscles of blood- 

 vessels, esophagus, stomach, intestine, bronchi, and others. 



Most viscera possess a double innervation from the thoracic- 

 lumbar sympathetic system and from the midbrain, bulbar, or 

 sacral system (see p. 229). For instance, the heart-beat is 

 accelerated by the thoracic-lumbar system and inhibited by the 

 bulbar system through the vagus; and the iris is contracted 

 through the midbrain sympathetic, but dilated through the 

 thoracic by way of the superior cervical ganglion (p. 211). 



Organs of Circulation. The nervous control of the heart 

 and blood-vessels is far too complex for full description here. A 

 few general features only can be touched upon. 



The rate of blood flow may be varied for the body as a whole 

 by changes in the rate and force of the pulsations of the heart, 

 and for particular parts of the body by changes in the caliber 

 of its blood-vessels. The heart beats automatically, but its 



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