302 THE RHOMBENCEPHALON. 



je's cells which enter into the descending cerebellar tract (?) 

 (see cerebellum, page 264). 



The restiform body is inclosed between the vestibular and coch- 

 lear roots of the auditory nerve (eighth) (Fig. 89). Ventral to 

 it and between the roots, is the ventral part of the cochlear nu- 

 cleus ; on its lateral surface and among the fibers of the lateral 

 root, is the dorsal, or lateral part of the same nucleus. The ves- 

 tibular nuclei the chief dorso-medial nucleus (Schwalbe), the 

 dorsolateral (Deiters), the superior (Flechsig and Bechterew) and 

 the nucleus of the descending root are situated dorsal and medial 

 to the restiform body. 



Tractus Solitarius (Figs. 92 and 94). The solitary tract is a 

 small, round bundle imbedded in the middle of the ventricular 

 gray matter of the posterior area. In Weigert-Pal sections of 

 the upper medulla it is clearly visible to the naked eye. It is 

 formed by the sensory roots of the nervus intermedius and the 

 ninth and tenth cerebral nerves. It descends through the nu- 

 cleus tractus solitarii lateral to the nucleus of the ala cinerea, and 

 along the medial aspect of the posterior columna of gray matter 

 in the cord. It ends on both sides of the median line in gelat- 

 inous gray matter, called the nucleus of the solitary tract, which 

 surrounds it. The nuclei of these tracts converge downward; 

 according to Cajal, they are united near their inferior extremities 

 by a central mass, called the nucleus commissuralis (Barker). 

 The solitary tract may be traced from the upper part of the me- 

 dulla down to the spinal cord (Kolliker). It is believed to asso- 

 ciate the nuclei of the nerves controlling respiration, hence the 

 synonym, respiratory bundle. 



GRAY MATTER OF MEDULLA. 



The gray matter of the medulla is composed (i) of that continu- 

 ous with the nucleus pontis, called the arcuate nucleus; (2) of the 

 ventricular gray substance, the stratum nucleare, and that of the 

 substantia reticularis, also continued downward from the pons; 

 and (3) of the special nuclei of the medulla, which are not repre- 

 sented in the pons or in the spinal cord. 



(i) Nucleus of the External Arcuate Fibers (Figs. 92 and 



