356 THE NERVE SYSTEM 



In front and behind it is marked by the continuation 

 of the anterior and posterior median fissures of the 

 cord, the former, with its process of pia mater, ending 

 in a cul-de-sac just below the pons, the foramen cecum. 

 The posterior expands into the fourth ventricle. 



Each lateral half of the medulla is divided into 

 areas. 



THE AREAS OF THE MEDULLA OBLONGATA. These 

 are: (1) Ventral area; containing the pyramid. (2) 

 Lateral area; containing the lateral tract olive. (3) 

 Dorsal area; containing the funiculus gracilis, funiculus 

 cuneatus, funiculus lateralis, and tuberculum cinereum. 



The restiform body succeeds the gracile and cuneate 

 nuclei in the dorsolateral part of the medulla oblongata. 

 Its fibers converge from various sources and ultimately 

 enter the cerebellum as its inferior peduncle. (Gray.) 



The Decussation of the Pyramids. It is a term 

 applied to the interlacing bundles seen on the ventral 

 aspect of the medulla, at the junction of the medulla 

 and the spinal cord. Ninety per cent, of the fibers 

 cross the median line in this decussation to continue 

 as the crossed pyramidal tract. 



STRUCTURE OF THE MEDULLA OBLONGATA. Gray 

 and white matter are constituents of the medulla; 

 the former is, in the internal part, continuous with 

 the gray substance of the cord, while the white 

 substance is external. 



The Gray substance of the medulla, examined under 

 the microscope, presents numerous groups of nerve 

 cells similar in arrangement to the cells in the spinal 

 cord, but they are not so regular, due to the changed 

 course of the fibers of the white substance. These 

 nerve cells are supported by neuroglia and connective 

 tissue. The nerve cells give off axones which ascend 

 to the brain and descend to the cord, conveying nerve- 

 impulses to the brain (sensor or conscious), and 

 transmitting other impulses from the brain to the 



