142 [Chap. XVII. 



CHATTER XV 11. 



THE MEDULLA OBLONGATA OR BULB. 



134. As the cervical portion of tlie cord passes 

 into the medulla oblongata, its parts alter position, 

 arrangement, and name in the following manner : 



(a) The anterior median fissure is continued as 

 far as the medulla extends. The posterior fissure of 

 the cord is also continued on the medulla, but in the 

 upper portion is lost, owing to the fact that the 

 central canal, which in the cord is situated in about 

 the middle, shifts in the medulla towards the posterior 

 surface, and soon altogether opens into the fourth 

 ventricle. 



185. (b) The tracts of white matter bordering the 

 anterior median fissure of the medulla, and separated 

 from the other tracts by a distinct fissure on the 

 surface, are the pyramidal tracts. As was mentioned 

 on a former page, the median portion of the anterior 

 columns of white matter of the cord i.e., the un- 

 crossed or direct anterior fasciculus is a direct pro- 

 longation of the pyramidal tract, and can be followed 

 in this upwards into the pyramids i.e., the oblong 

 prominences in the upper part of the medulla next 

 to the anterior median fissure and thence to the 

 pons Yarolii and farther into the crus cerebri. 

 A major portion of the pyramidal tract crosses in 

 the lower portion of the medulla, in tlje anterior 

 median fissure this forms the pyramidal decussation 

 (Fig. 88). These crossed bundles enter the postero- 

 lateral column of the cord, that part of it which has 

 been mentioned above as the fasciculus of Turk. The 

 crossed portion of the pyramidal tract passes into 



