6l2 THE NERVOUS SYSTEM 



and in the inter-olivary region enter the mesial fillet, which passes upward 

 through the pons to end about the cells in the mid-brain and in the optic 

 thalami. These fibers are probably augmented by the addition of fibers 

 from the anterior columns of the cord, and by fibers arising from cells in the 

 sensory nuclei of the cranial nerves ending in the bulb. 



b. External arcuate fibers, after decussating in the same way, pass out- 

 ward superficially over the anterior pyramid and olivary body, reaching the 

 restiform body and passing to the side of the cerebellum opposite to their 

 nuclei of origin. These fibers appear to be interrupted, at least in part, in 

 the external arcuate nuclei. They connect one side of the spinal cord with 

 the opposite side of the cerebellum through the gracile and cuneate nuclei. 



c. Direct lateral fibers pass to the restiform body and so to the same side 

 of the cerebellum. 



2. Fibers from the olivary body pass to the opposite side of the cerebellum 

 through the reticular formation and restiform body. 



3. Fibers from the vestibular nucleus of the eighth or auditory nerve in 

 the floor of the fourth ventricle pass to the same side of the cerebellum. 



FUNCTIONS OF THE MEDULLA. 



The medulla is of great importance in the physiological economy of 

 the body. Its functions can be classified in three groups. First should be 

 given the function of conduction between the cord and the higher centers 

 of the brain. Second, the medulla is a center of numerous reflex activities, 

 especially those regulating the vital functions of the body, such as respiration, 

 circulation, and the like. A third function of centers in the medulla is that 

 of automatic activity. 



The Medulla as a Conducting Path. The medulla is the pathway 

 of all ascending and descending nerve impulses between the spinal cord and 

 most of the peripheral sensory and motor apparatus on the one hand, and the 

 cerebellum and the cerebral centers on the other. These conducting paths 

 are described in the tracts that have already been discussed at some length. 

 They are represented graphically in the diagrams, figures 379, 382, and 388. 



Reflex Centers of the Medulla. The larger number of the cranial 

 nerves, as we shall presently see, take their origin from the medulla and 

 pons. Some of these nerves have both sensory and motor roots, while 

 others are either exclusively motor or sensory. A large percentage of the 

 afferent or sensory impulses that enter the medulla produce reflex effects 

 on the motor nuclei so richly represented in the medulla. The nuclei, or 

 centers, regulating some of the most important functions of the body are 

 among those in this group. When certain of these centers are interfered 

 with, death follows. 



Life may continue when the spinal cord is cut away in successive portions 



