THE STRUCTURE OF THE MEDULLA OBLONGATA 145 



tudinal nerve-fibers belonging to the medial lemniscus, tectospinal tract, and the 

 medial longitudinal fasciculus (Fig. 105). The latter is closely associated with 

 the vestibular nerve and can best be described with the central connections of 

 that nerve. Theformatio reticularis grisea is found dorsal to the olive and lateral 

 to the hypoglossal nerve. In it the nerve-cells predominate and the trans- 

 versely coursing internal arcuate fibers form a conspicuous feature. Its longi- 

 tudinal fibers, though less prominent, are of great importance. The descend- 

 ing fibers include those of the rubrospinal tract, which can be followed into the 

 lateral funiculus of the spinal cord, and the thalamo-olivary fasciculus, which 

 ends in the olive. Among the ascending filers are those of the ventral and 

 dorsal spinocerebellor, the spinothalamic , and spinotectal tracts. 



The neme-cells of the reticular formation are scattered through the mesh of 

 interlacing fibers. In certain localities they are more closely grouped and form 

 fairly well-defined nuclei. Among these we may select two for special atten- 

 tion. The lateral reticular nucleus or nucleus of the lateral funiculus is a long 

 column of cells found along the deep surface of the ventral spinocerebellar tract, 

 from which it is said by Andre Thomas to receive afferent fibers. At any rate, 

 it receives fibers from the lateral funiculus of the spinal cord (Cajal, 1909) and 

 sends its axons to the cerebellum by way of the restiform body (Van Gehuchten, 

 1904; Yagita, 1906). It seems, therefore, to be a way station on a sensory 

 path from the spinal cord to the cerebellum. Some large cells in the gray part 

 of the reticular formation may be grouped together and called the motor nucleus 

 of the tegmentum (nucleus magnocellularis of Cajal). Their axons become as- 

 cending or descending fibers or may bifurcate into ascending and descending 

 branches within the reticular formation. Kohnstamm has traced such fibers 

 by means of the degeneration method, and has shown that they run for the 

 most part in a caudal direction and that some of them reach the cervical por- 

 tion of the spinal cord (tractus reticulospinalis Fig. 115). 



The nuclei of the cranial nerves can best be considered in a separate chapter. 

 At this point it will only be necessary to enumerate and locate the nuclei of those 

 nerves which take origin from the medulla oblongata. 



The nucleus of the hypoglossal nerve contains the cells of origin of the 

 motor fibers which compose that nerve. It forms a long column of nerve-cells 

 on either side of the median plane in the ventral part of the gray matter sur- 

 rounding the central canal and in the floor of the fourth ventricle (Figs. 99, 101, 

 103). In the latter region it lies immediately beneath that part of the floor 

 which was described in the preceding chapter under the name of the trigonum 



