302 HUMAN ANATOMY. 



THE INTERNAL STRUCTURE OF THE MEDULLA OBLONGATA. 



The anterior and lateral pyramidal tracts of the cord are 

 continued into the medulla oblongata as the pyramids. The 

 lateral pyramidal tracts decussate in the lower part of the me- 

 dulla. 



The anterior ground bundle is continued upward into the 

 medulla as the posterior longitudinal bundle. It lies behind the 

 pyramids in the medulla. 



The sensory columns of the cord (Goll and Burdach) are 

 continued into the medulla oblongata as the funiculus gracilis 

 and cuneatis. They increase in size and each develops a nucleus : 

 the clava and cuneate nucleus, respectively. These fibres partly 

 form the restiform bodies. 



The decussation of the sensory fibres takes place at a higher 

 plane than that of the motor fibres. It is also called the decus- 

 sation of the fillet and it consists of the decussating fibres derived 

 from the clava and the cuneate nucleus. These fibres are called 

 deep arcuate fibres. After decussating the fibres are continued 

 upward behind the pyramids, displacing backwards the posterior 

 longitudinal bundle. 



In the medulla on cross-section are seen the olivary bodies,, 

 which contain the dentate nuclei. 



The restiform bodies, or inferior cerebellar peduncles are 

 formed by the direct cerebellar tract, the posterior superficial 

 arcuate fibres, the anterior superficial arcuate fibres, and the 

 cerebello-olivary fibres. 



The formatio reticularis is seen behind the pyramids and 

 the olivary bodies in the medulla oblongata. It is composed of 

 the deep arcuate fibres, fibres of Gower's tract, and the antero 

 lateral ground bundle. 



The gray matter of the cord is continued into the medulla. 

 The anterior horns are cut off and displaced by the decussation of 

 the lateral pyramidal tract and the posterior horns are displaced 

 outward by the increase in size of the posterior sensory tracts. 

 The latter are known as the nucleus of Rolando and are capped 

 by the substantia gelatinosa Eolandi. 



The central canal is expanded into the fourth ventricle. 

 The gray matter forms nuclei for the cranial nerves in the floor 

 of the fourth ventricle. 



