THE BRAIN/ 393 



nucleus of the tenth nerve. This bundle represents 

 fibers from the ninth and tenth nerves. Just in- 

 ternal or mesial to this bundle are a few cells called' 

 the solitary nucleus. This is probably a motor nu- 

 cleus of the ninth and tenth nerves. Lateral to the 

 solitary fasciculus are the fibers of the large restiform 

 body on their way to the cerebellum. 



The posterior longitudinal bundle is a tract of 

 nerve fibers that appears in cross section just an- 

 terior to the nucleus of the twelfth nerve, and lies in 

 close apposition to the median plane. The formatio 

 reticularis occupies the greater part of the center of 

 each lateral half of the medulla, and presents the 

 same appeareance as in sections of the closed med- 

 ulla. Likewise the cells of the olivary body, which 

 in the open medulla form a large conspicuous nu- 

 cleus that takes the form of a U with wavy sides, and 

 with the open extremity turned inward and upward. 

 Nerve fibers from its hilum sweep across to the oppo- 

 site side and some curve around to join the super- 

 ficial arcuate fibers of the same side. 



The arcuate fibers are divided into the deep and 

 the superficial set. The deep set come from the nuclei 

 cutieatus and gracilis and from the sensory nuclei of 

 the cranial nerves. From this source they arch to 

 the opposite side and then turn to pass upward in 

 the brain stem, where they form the middle fillet. 

 The superficial set may be divided into an anterior 

 and a posterior group. The anterior group originate 

 in the nuclei gracilis and cuneatus, accompany the 

 deep set to the opposite side of the medulla, where 

 some of them become superficial in the anterior 

 mesial fissure, then curve around the anterior pyra- 



