628 



NERVOUS SYSTEM. 



two anterior pyramids, one on either side. Viewed superficially, the inner- 

 most fibres of these pyramids are seen to decussate in the median line ; but 

 if the fibres be traced from the cord, it is found that they come from the 

 crossed pyramidal tracts of the lateral columns and that none of them are 

 derived from the anterior columns. The fibres of the external portion of 

 the anterior pyramids come from the direct pyramidal tracts of the cord. 

 At the site of the decussation, the pyramids are composed entirely of white 



matter ; but as the fibres spread out to pass to 

 the encephalon above, they present nodules of 

 gray matter between the fasciculi. 



External to the anterior pyramids, are the 

 corpora olivaria. These are oval and are sur- 

 rounded by a distinct groove. They are white 

 externally and contain a gray nucleus called 

 the corpus dentatum. 



External to the corpora olivaria, are the 

 restiform bodies, formed chiefly of white mat- 

 ter and constituting the postero-lateral portion 

 of the medulla. They are continuous with 

 the posterior white columns of the cord. The 

 restiform bodies spread out as they ascend, 

 and pass to the cerebellum, forming a great 

 portion of the inferior peduncles. Some fibres 

 from the restiform bodies pass to the cere- 

 brum. 



Beneath the olivary bodies and between 

 the anterior pyramids and the restiform bod- 

 ies, are the lateral tracts of the medulla, some- 

 times called the intermediary or lateral fascic- 

 view of the medulla uli, or the funiculi of Rolando. These are 



oblongata (Sappey). . . 



i, infundibuium ; 2, tuber cinereum ; composed of an intimate mixture of white and 



gray matter and have a yellowish-gray color. 

 They receive all that portion of the antero- 

 lateral columns of the cord which does not 

 enter into the composition of the anterior 

 dtSSSf M u PJ^mids. They are usually described as parts 

 ! ?hiasm c of d kl 5 ' optic of the restiform bodies, but they are peculiarly 

 nerves 17, motor ocuiicommunis; important, from the fact that they contain 



18, patheticus ; 19, fifth nerve ; 20, J 



motor ocuii externus ; 21, facial the gray centre presiding over respiration ; 



nerve : 22, auditory nerve ; 23, nerve c J 



ofwrisberg;24,giosso-pharyngeai and for that reason they are here described as 



nerve ; 25, pneumogastric ; 26, 26, . . . * 



spinal accessory ; 27, sublingual distinct f aSClCUU. 



nerve ; 28, 29, 30, cervical nerves. . . ,.-,. ., x 



Ine posterior pyramids (luniculi graciles) 



are the smallest of all. They pass upward to the cerebellum, without decus- 

 sating, joining the restiform bodies above. They are composed chiefly of 

 white matter. As they pass upward in the medulla, they diverge, leaving a 

 space at the fourth ventricle. 



