540 THE NERVOUS SYSTEM 



pyramidal tracts connect the bulb with the cerebrum ; and the direct cerebellar 

 and the antero-lateral ascending tract, tract of Gowers, connect it with the 

 cerebellum. Other connections of the bulb with the cerebrum and with 

 the cerebellum are: 



1. Fibers from the nucleus gracilis and nucleus cuneatus, which, as we 

 have said, are the endings of the fibers cf the columns of Goll and Burdach 

 of the cord, pass in sets in the following manner: 



a. Internal arcuate fibers pass down and inward to the opposite side in 

 the reticular formation, composing in part the superior or sensory decussation, 

 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 outward 

 superficially over the anterior pyramid and olivary body, reaching the resti- 

 form 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 Oblongata. The chief functions of the 

 medulla are those of carrying impulses, i.e., conduction, between the cord and 

 brain; of carrying on activities distinctly reflex in character; and of producing 

 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 380 and 396. 



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 motor or sensory exclusively. 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 



