THE MEDULLA OBLONGATA 253 



peduncles of the cerebellum form the lateral boundaries of the 

 superior triangle. The inferior triangle is covered by the cere- 

 bellum; the superior by the valve of Vieussens, which stretches 

 between the superior peduncles. This ventricle communicates 

 above with the third ventricle by the aqueduct of Sylvius, or the 

 iter a tertio ad quartum ventriculum; below, with the central canal 

 of the cord and with the subarachnoid space. The floor of the 

 ventricle presents a longitudinal median fissure and numerous 

 small elevations indicating the position of the nuclei of origin of 

 certain of the cranial nerves. 



The gray matter of the medulla has the same general distri- 

 bution as that in the cord, but is by no means so regular in its 

 disposition. The direction of the white fibers is not so uniform 

 as in the cord. They run not only longitudinally, but trans- 

 versely to connect the lateral halves, and in other directions to 

 connect various centers situated in this part of the encephalon 

 and to connect the medulla with other parts of the brain. The 

 following is the relation of the columns of the cord to the medulla: 



The direct and crossed pyramidal tracts pass to the encephalon 

 constituting, in the medulla, the anterior pyramids the direct, 

 having decussated below, occupying here the outer portion of 

 the pyramid, and the crossed decussating in the medulla, and 

 occupying the inner portion of the pyramid. 



Those columns concerned in reflex action, the anterior funda- 

 mental fasciculi, the anterior root zones, and the mixed lateral 

 tracts do not continue farther upward than the gray matter of 

 the medulla. 



The columns of G oil are continuous with the funiculi graciles. 



The columns of Burdach and the direct cerebellar fasciculi pass 

 to the cerebellum through the restiform bodies of the medulla. 



Functions. The functions of the medulla are (i) conduction, 

 (2) reflex action, (3) to furnish centers for special acts. 



i. As a conductor the medulla is absolutely necessary as a 

 means of connection between the brain and cord. Sensory im- 



