THE MEDULLA OBLONGATA 21 



presents a transversely striated appearance, which indicates the 

 direction taken by its superficial fibres (Fig. 12). The dorsal 

 surface of the pons forms the upper part of the floor of the 

 fourth ventricle (Fig. 32). 



The fifth, sixth, seventh and eighth cerebral nerves are all 

 connected with the anterior surface of the pons. The 

 fifth emerges from the brain-stem near the upper border of 

 the pons, at its junction with the brachium pontis. The 

 sixth emerges near the median plane, in the groove between 

 the pons and the medulla oblongata. The seventh and eighth 

 are connected to the same groove but lie farther away from 

 the median plane (Fig. 8). 



The Medulla Oblongata connects the pons above to the 

 spinal medulla below. Its anterior surface is marked by two 

 elongated elevations, which are termed the pyramids. They 

 lie one on each side of the median plane and they are produced 

 by the underlying pyramidal tracts. At a lower level the 

 superficial part of the decussation of the pyramids can some- 

 times be made out in the median plane (Fig. 12). A second 

 elevation is situated lateral to the pyramid and separated 

 from it by a groove in which the fibres of the twelfth (hypo- 

 glossal'] nerve emerge. It is termed the olive, and is produced 

 by a mass of grey matter, known as the olivary nucleus. The 

 restiform body forms a surface elevation on the lateral aspect 

 of the medulla oblongata. It is separated from the olive by 

 a longitudinal groove, in which the fibres of the ninth, tenth 

 and eleventh cerebral nerves emerge from the brain-stem. 

 (Fig. 8). Most of the tracts which constitute the restiform 

 body pass upwards into the cerebellum. 



The dorsal surface of the medulla oblongata in its upper 

 part forms the lower portion of the floor of the fourth 

 ventricle. 



The Cerebellum lies in the posterior cranial fossa below the 

 posterior, parts of the cerebral hemispheres, from which it is 



