424 HISTOLOGY 



side the cerebellum connects with three bundles of fibers, which come 

 together to form its medulla (corpus medullare). The medulla is sur- 

 rounded by the gray cortical substance, and the entire cerebellum is 

 divided into many lobes and lobules. 



The cavity of the hind-brain, which is continous posteriorly with the 

 central canal of the cord, and anteriorly with the cerebral aqueduct, 

 is known as the fourth ventricle. It extends upward toward the medulla 

 of the cerebellum, forming a tent-like recess, the apex of which is the 

 fastigium. 



Myelencephalon. The myelencephalon becomes the medulla oblon- 

 gata, continuous without demarcation with the medulla spinalis or spinal 

 cord. The ventral median fissure becomes shallow, but it may be traced 

 to the pons (Fig. 435, B). On either side of its upper portion, there is an 

 elongated swelling, the pyramid, corresponding in position with the 

 ventral funiculus of the cord. Each pyramid is bounded laterally by 

 the ventro-lateral groove, from which the motor roots of the hypoglossal 

 nerve emerge; this groove is continuous with the ventro-lateral groove of 

 the cord, from which the motor roots of the spinal nerves proceed. Near 

 the pons the abducent nerve comes out close beside this groove. The 

 dorso-lateral groove of the cord likewise extends to the pons; and in line 

 with the dorsal, roots of the cord, the sensory roots of the vagus, glosso- 

 pharyngeal, acoustic and facial nerves enter this groove. The lateral 

 roots of the accessory, glossopharyngeal and facial nerves emerge just 

 below them. The space between the ventro-lateral and dorso-lateral 

 grooves corresponds with the lateral funiculus of the cord. Toward the 

 upper end of the medulla, it presents a rounded swelling known as the 

 olive (Fig. 435, B). 



The dorsal funiculus of the upper part of the cord is divided into the 

 medial gracile and lateral cuneate fasciculi; these may be followed into 

 the medulla where they become broader (Fig. 435, A). Some of their 

 fibers enter the restiform body, and pass to the cerebellum; others pass 

 downward on either side of the central canal and continue beneath the 

 floor of the fourth ventricle to the hemispheres. Where the central canal 

 expands to become the thin-roofed fourth ventricle, all nerve fibers either 

 pass downward into its floor, or turn aside to enter the restiform body. 



MEDULLA OBLONGATA. 



The study of the medulla oblongata requires full consideration of the 

 fiber tracts of the cord and anterior portion of the brain, which cannot here 

 be taken up; only a few of the most fundamental features of the medulla 

 are to be mentioned. Sections through the lower end of the medulla re- 

 semble those of the cord, and the gray substance retains the form of 



