THE VISCERAL AND GUSTATORY APPARATUS 247 



eyeball in the ciliary process and iris. These fibers are involved 

 in the movements of accommodation of the eye for distance and 

 in the regulation of the diameter of the pupil. The nucleus of 

 the fasciculus solitarius is connected through the reticular forma- 

 tion with all of the motor centers of the medulla oblongata for 

 the reactions of mastication and swallowing and for many other 

 movements ; from this nucleus there is a descending tract to the 

 motor centers of the spinal cord, the tractus solitario-spinalis 

 (Figs. 112 and 113). There is also a connection with the supe- 

 rior and inferior salivatory nuclei of the VII and IX nerves. 

 The excitation of the gustatory fibers of these nerves by the 

 presence of food in the mouth is carried to the nucleus of the 

 fasciculus solitarius and thence through the reticular formation 

 to the salivatory nuclei, from which the flow of saliva is excited. 

 There are other connections with the motor centers of the spinal 

 cord through the descending fibers of the fasciculus solitarius, 

 some of these fibers crossing to the opposite side in the vicinity 

 of the commissural nucleus of Cajal (Fig. 114). 



Summary. The cerebro-spinal visceral systems fall into a 

 general group related peripherally to the sympathetic nerves and 

 a special group independent of the sympathetic. 'The second 

 group includes the apparatus for taste and probably for smell. 

 The central innervation of the viscera is partly from the spinal 

 and midbrain regions, but chiefly from the visceral area of the 

 medulla oblongata. The heart and blood-vessels have a double 

 innervation derived from both the spinal and the bulbar visceral 

 centers, and the nervous control of the organs of circulation is 

 very complex. Respiration in lower vertebrates is effected by 

 strictly visceral structures and is controlled from the visceral 

 area of the medulla oblongata. In mammals the muscles of 

 ordinary respiration are all of the somatic type, but the centers 

 of control are retained in the visceral area of the oblongata. The 

 sensations related to the digestive tract are served chiefly 

 (though not exclusively) by the vagus. There are special sali- 

 vatory nuclei related to the VII and IX cranial nerves. The 

 nerves of taste are the VII, IX, and to a very limited extent (in 

 man) the X pairs of cranial nerves. The primary cerebral gus- 

 tatory center is in the upper part of the nucleus of the fasciculus 

 solitarius, but the cortical path is unknown. 



