ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 



623 



in its long course in the cord gives off fibers in succession which go 

 either into the cells of the anterior horn or into the crossed pyra- 

 midal tract of the opposite side. The commissure also contains 

 fibers which unite transversely the anterior horns of the two sides. 



The gray, or posterior, commissure is likewise formed by decussa- 

 tions upon the median line both in front of and back of the central 

 canal. The fibers comprising this decussation are: some of the 

 fibers from the posterior roots on one side to terminate in the 

 opposite posterior horn; also, fibers of the posterior horn which go 

 into the deep lateral tract. 



Fig. 239. Medulla Oblongata, Pons, Cerebellum, and Pes Pedunculi. 

 Anterior View, to Demonstrate Exits of Cranial Nerves. (EDINGER. ) 



Medulla Oblongata. 



The medulla oblongata is a continuation of the spinal cord 

 rhich crowns its upper part in the form of a capital. It reaches 

 from the cord to the pons Varolii. The medulla is an enlargement 

 in the form of a truncated cone, a little flattened from before back- 

 ward. It measures an inch in length, about three-fourths in width, 

 id about one-half inch in thickness. Commencing toward the mid- 

 lie part of the odontoid process, it inclines forward, to recline upon 

 the basilar process of the occipital bone. The medulla forms with 

 le cord an obtuse angle open in front. 



