202 LECTURES ON THE CENTRAL NERVOUS SYSTEM. 



spinal cord.. Externally this is covered by a bundle of fibres, 

 which is separated into numerous fasciculi, and which has ac- 

 companied it from the upper cervical cord. This bundle has 

 become somewhat larger near its upper extremity, and can be 

 traced high up into the pons. There it associates itself with 

 the emerging fibres of the trigeminus, and perhaps, too, enters 

 into some relation with their nucleus. This bundle, the ascend- 

 ing root of the trigeminus, has been described before (Fig. 109). 



The region between the olivary bodies and the nuclei of 

 the posterior columns, bounded externally by the direct lateral 

 cerebellar tract and the ascending root of the fifth nerve and 

 internally by the lemniscus, contains, besides the numerous inter- 

 nal arciform fibres, a great number of short fibres whose course 

 can be traced but a short distance. Scattered throughout them 

 are numerous multipolar ganglion-cells. We call this function- 

 ally unknown formation the formatio reticularis, and the space 

 occupied by it the motor area of the tegmentum. Masses of 

 cells are found in this situation in all vertebrates. They can be 

 traced as scattered groups of cells up to the line of the raphe. 

 As long as we possess no information concerning them, we shall 

 do well to adopt the name given them by Bechterew, nucleus 

 reticularis f egmenti. 



The fibres of the antero-lateral columns, which do not 

 enter the layer of the fillet, can be traced into the formatio 

 reticularis. It is possible, however, that they pass higher up. 



On making further sections through the oblongata the 

 picture changes but little for about two millimetres. We see 

 the sensory nucleus of the vagus and giosso-pharyngeal project- 

 ing far upward, and continually sending off root-fibres toward 

 the periphery from its own ventral surface. The ascending root 

 also gives off an occasional rootlet to join the latter. The 

 greatest change is in the restiform body, which increases greatly 

 in size, for at this level it has begun to receive the fibres passing 

 from the cerebellum to the olivary body. 



The sections made just before reaching the pons show (Fig. 



