WHITE MATTER OF MEDULLA. 293 



The root-bundles of the eighth to the twelfth cerebral nerves 

 constitute the remaining groups of dorso-ventral fibers. By 

 them the medulla is divided into areas. 



(b) The root-bundles of the hypoglossal nerve (Fig. 93) run from 

 the ventricular gray matter, near the median line, ventro-lateral- 

 ward to the anterior lateral sulcus, where they emerge. Inclosing 

 between them and the raphe, the anterior area, they also separate 

 it from the lateral area. The anterior and lateral areas are bounded 

 dorsally by the thick sheet of gray matter in the floor of the 

 fourth ventricle. 



(c) The vestibular root of the auditory nerve, the roots of the 

 glosso-pharyngeal and vagus and the cerebral root of the accessory 

 nerve form the third group of dorso-ventral fibers (Fig. 93). 



The motor fibers of the ninth, tenth and cerebral part of the 

 eleventh nerves take their origin in nuclei of the medulla and 

 emerge from the posterior lateral sulcus; while the sensory fibers 

 of the vagus, glossopharyngeal and vestibular nerves enter that 

 sulcus from without and run through the medulla to their terminal 

 nuclei in the ventricular gray matter. These nuclei, both genetic 

 and terminal, are located lateral to the hypoglossal nucleus. 

 The nerve roots rising or terminating in them separate the lateral 

 from the posterior area. The posterior area comprises everything 

 dorsal to the above roots of the eighth to eleventh cerebral nerves. 

 It thus includes the gray matter in the floor of the fourth ventricle, 

 called the stratum nucleare. 



(3) Longitudinal Fibers. In the medulla, the longitudinal 

 fibers, are chiefly continuations of the same in the pons and the 

 restiform bodies; they are also continuous with the tracts of the 

 spinal cord. They can be best located by reference to the three 

 areas bounded by the above dorso-ventral fibers, namely, anterior, 

 lateral and posterior areas, which are distinctly outlined in the 

 upper half of the medulla (Figs. 92 and 93). 



Longitudinal Fibers of the Anterior Area. The anterior 

 area of the medulla lies betwen the raphe and the roots of the 

 hypoglossal nerve, and between the anterior surface and the gray 

 matter in the floor of the fourth ventricle (Figs. 92 and 93). It 

 contains the pyramid, the medial fillet, the medial and anterior 



