THE MEDULLA OBLONGATA AND BRAIN. 22$ 



becoming permeated by bands of nerve fibres. This arrange- 

 ment, the so-called formatio reticularis, gradually extends 

 over nearly the whole medulla oblongata. 



Connected masses of gray substance form what has been 

 called " nuclei." A portion of these are the centres of escap- 

 ing nerves ; in others, systems of fibres of the medulla ob- 

 longata acquire a provisory termination, to become modified 

 at these places, and subsequently pass further on with their 

 derivatives. Among the latter, the so-called "specific nuclei," 

 are included the superior and inferior olivary bodies, the 

 Deiters' nucleus, the pyramidal nucleus, the ganglia post 

 pyramidalia, the gray substances of the pons Varolii, and in 

 further extension also, the corpus dentatum cerebelli, the 

 gray masses of the crura cerebelli, and the greater portion of 

 the eminentia quadrigeminae (Deiters). 



There is besides a transverse, arched and circular system 

 of fibres, Arnold's stratum zonale. 



In the formatio reticularis, as well as in the nuclei, we meet 

 with ganglion cells of the most varied form, and in part of 

 considerable size, with axis cylinder and protoplasma pro- 

 cesses. In consequence of the penetration of the gray sub- 

 stance into the funiculus gracilis, the floor of the fourth ventri- 

 cle is almost exclusively formed of gray substance. The 

 neuroglia which surrounded the axis canal of the spinal cord 

 also undergoes a proliferous increase to subsequently form a 

 considerable share of the walls of the aqueductus Sylvii, the 

 third ventricle and the infundibulum. 



Now, how do the cerebral nerves arise from the medulla 

 oblongata ? 



Deiters found here not only an anterior and a posterior 

 centre of origin, as in the spinal cord, but also a third lateral 

 one. The latter begins in this organ, at the anterior horn, 

 and gradually acquires a mixed character. 



From it arise the accessorius, vagus, glosso-pharyngeus, 

 facialis, acusticus and anterior trigeminus root. 



The sensory portion of the trigeminus is said to be derived 



from the posterior system of origin. 

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