THE NERVOUS SYSTEM. 593 



to the pyramidal tracts connecting the bulb with the cerebrum and the 

 direct cerebellar and the antero-lateral ascending tract connecting it 

 with the cerebellum, there are other connections of the bulb with the 

 cerebrum, and with the cerebellum, not actually direct. 



(1.) Fibres from the nucleus gracilis and nucleus cuneatus, which, 

 as we have said, are the bulbar endings of the fibres of the postero- 

 median and postero-external columns of the cord, pass in sets as it were 

 in the following manner : 



(a.) Internal arcuate fibres. Some pass down and inward to the other 

 side in the reticular formation, forming in part the superior or sensory 

 decussation, and in the inter-olivary region become longitudinal in a 

 band of fibres called ihe fillet, which passes upward. These fibres are 

 probably augmented by the addition of fibres from the anterior columns 

 of the cord. 



(b.) External arcuate fibres also decussate in the same way, pass 

 down along the anterior fissure, and then running outward superficially 

 over the anterior pyramid and olivary body, reach the restiform body 

 and pass to the side of the cerebellum opposite to their nuclei of origin. 

 These fibres appear to have some relation with the external arcuate nu- 

 clei. They connect one side of the spinal cord with the opposite side of 

 the cerebellum through the gracile and cuneate nuclei. 



(c.) Direct lateral fibres pass to the restiform body and so to the same 

 side of the cerebellum. 



(2.) Fibres from the olivary body pass to the opposite side of the 

 cerebellum probably through the reticular formation. 



(3.) Ar cif or m fibres. Fibres from the nucleus of the 8th or auditory 

 nerve in the floor of the 4th ventricle, pass to the same side of the cere- 

 bellum. 



FUNCTIONS OF THE BULB OR MEDULLA OBLONGATA. 



The functions of the bulb are those of, (a.) conduction; (b.) reflex 

 action; and (c.) automatism. 



(a.) Conduction. As a conductor of impressions, the medulla oblon- 

 gata has a wider extent of function than any other part of the nervous 

 system, since it is obvious that all impressions passing to and fro be- 

 tween the brain and the spinal cord must be transmitted through it. 



(b.) Reflex Action. As a nerve centre by which impressions are 

 reflected, the medulla oblongata also resembles the spinal cord ; the only 

 difference between them consisting of the fact that many of the reflex 

 actions performed by the former are much more complicated than any 

 performed by the spinal cord. 



It has been proved by repeated experiments on the lower animals 

 that the entire brain may be gradually cut away in successive portions, 

 38 



