384 ANATOMY OF THE CENTRAL NERVOUS SYSTEM. 



thick, much separated bundle of meduUated fibers, which are found in its- 

 vicinity from the upper cervical cord, grovfing larger as they ascend. This 

 bundle can be traced as high as the pons. There it joins vi'ith the trigeminal 

 fibers just issuing. Eegarding this spinal root of the trigeminus, cf. page 364. 



The territory between the olive and the nuclei of the posterior columns,, 

 bounded externally by the lateral cerebellar tract and the ascending trigem- 

 inal root and internally by the fillet, contains, besides the numerous fibrse 

 arciformes internse a number of short fibers, and, lying between these, scat- 

 tered multipolar nerve-cells. 



The reticular appearance of the bundles of fibers in a cross-section of 

 the medulla justifies the appellation substantia reticularis. The group of 

 cells have been named nucleus reticularis tegmenti by Bechterew, and it can 

 be traced upward to near the corpora quadrigemina. The cells and the 

 fibers are, as far as we now know, of the same character as the column-cells 

 in the cord; by their much divided axis-cylinders they join different levels 

 of the bulb together. And so the entire system found in the lateral columns 

 of the cord corresponds closely with this in the medulla. It is well, then, 

 to call this characteristic field of the elongated cord the association-field of 

 the medulla oblongata. It has already been mentioned (page 80) that upon 

 this wealth of association-fibers probably is dependent the property of the 

 oblongata to co-ordinate various functions, as it does. 



If one make other sections of the medulla higher up, the cross-section 

 does not change materially for about two millimeters. One sees that the 

 sensory nucleus of the pneumogastric, extending farther upward, continually 

 receives from the periphery root-fibers in its ventral aspect. From the fas- 

 ciculus solitarius the fibers of the glosso-pharyngeus pass in small bundles 

 near the frontal end of the vagus nucleus. The restiform body alone here 

 increases greatly in circumference. To it pass in this level the olivary fibers 

 from the cerebellum. 



The last sections before reaching the pons (Fig. 244) show that the pos- 

 terior columnar nuclei have disappeared, and in their place lies the thick 

 mass of fibers of the restiform body. To the inner side of it is a new set of 

 fibers cut transversely, the direct cerebellar sensory tract. Where it began is 

 hard to say; perhaps it already existed in the nuclei of the posterior columns. 

 Besides this, in this section we have a descending acusticus root. From the 

 corpus restiforme pass fibers to the inferior olive, which in this level is much 

 sm-aller than below. The lemniscus and the tegmentum occupy the same 

 positions as in the last-described sections. Three new nuclei have come to 

 view. One, occupying the place where lower down the motor fibers of the 

 vagus arose (Fig. 243), sends its fibers dorsally and inward, where they soon 

 collect in a bundle near the median line: the nucleus facialis. The second 

 of the three new nuclei lies external to the restiform body. At times we 



