GENERAL FEATURES 369 



Below the pons, in the vallecula between the hemispheres 

 of the cerebellum, is the medulla oblongata. Springing from 

 the sulcus between the medulla oblongata and the pons, are 

 the abducens, the facial, and the acoustic nerves, in that 

 order from the median plane to the lateral border, on each 

 side. 



The medulla oblongata is cleft, in the median plane, by an 

 anterior longitudinal fissure which is bounded, on each side, by 

 a longitudinal elevation called a pyramid. At the lateral side 

 of the upper part of each pyramid is an oval prominence 

 called the olive, and between the olive and the pyramid 

 lie the fila of the hypoglossal nerve ; whilst attached to the 

 sides of the medulla oblongata, a little dorsal to the olive, 

 are the fila of the glosso-pharyngeal, the vagus, and the 

 accessory nerves, in that order from above downwards. 



At the sides of the pons and the medulla oblongata are 

 the inferior surfaces of the hemispheres of the cerebellum. 



When the positions of the fila of origin of the cerebral 

 nerves have been noted, the hind-brain and the lower part 

 of the mid-brain should be removed. When that has been 

 done the posterior sections of the inferior surfaces of the 

 hemispheres will be exposed. They are separated from 

 each other, posteriorly, in the median plane, by the posterior 

 part of the longitudinal fissure, but they are united, more 

 anteriorly, immediately dorsal to the anterior part of the mid- 

 brain, by the splenium of the corpus callosum (Fig. 138). 



When the points mentioned above have been verified the 

 dissector should examine the dorsal aspect of the hind-brain, 

 which is formed by the cerebellum, and he should note that 

 it is separable into two hemispheres united by a median ridge 

 called the superior vermis. The antero- posterior length of 

 the superior vermis is not so great as the antero-posterior 

 length of the hemispheres ; therefore the hemispheres are 

 separated, anteriorly, by an anterior notch and, posteriorly, by 

 a posterior notch. 



The dissector should terminate his inspection of the general 

 features of the brain by gently separating the medulla oblongata 

 from the inferior aspect of the cerebellum, if he is dealing 

 with a specimen and not a cast ; when he has done that, he 

 will be able to convince himself that the roof of the cleft or 

 vallecula, in which the medulla oblongata lies, is formed by 

 the inferior part of the middle portion of the cerebellum, 



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