146 THE NERVOUS SYSTEM 



hypoglossi (Fig. 89). In reality, it corresponds only to the medial part of this 

 eminence, for on its lateral side there is found another group of cells known as 

 the nucleus intercalatus (Fig. 103). From their cells of origin the fibers of 

 the hypoglossal nerve stream forward through the reticular formation to emerge 

 at the lateral border of the pyramid. 



The nucleus ambiguus is a long column of nerve-cells which give origin to 

 the motor fibers that run through the glossopharyngeal, vagus, and accessory 

 nerves to supply the striated musculature of the pharynx and larynx. It is 

 located in the reticular formation of both the open and the closed portions 

 of the medulla, ventromedial to the nucleus of the spinal tract of the trigeminal 

 nerve (Figs. 101, 103). 



The dorsal motor nucleus of the vagus lies along the lateral side of the 

 nucleus of the hypoglossal. It occupies the ala cinerea of the rhomboid fossa 

 and extends into the closed part of the medulla oblongata along the lateral 

 side of the central canal (Figs. 89, 99, 101, 103). From the cells of this nucleus 

 arise the efferent fibers of the vagus nerve which innervate smooth muscle 

 and glandular tissue. The afferent fibers of the vagus and glossopharyngeal 

 nerves bend caudally and run within the tractus solitarius. 



The nucleus of the tractus solitarius is the nucleus of reception of the affer- 

 ent fibers of the facial, glossopharyngeal, and vagus nerves, i. e., it contains 

 the cells about which these afferent fibers terminate. The tractus solitarius 

 can be traced throughout almost the entire length of the medulla. It decreases 

 in size as the descending fibers terminate in the gray matter which surrounds 

 it (Figs. 92, 101, 103). 



