606 THE NERVOUS SYSTEM 



II. Mid-brain or mesencephalon. 



d. Corpora quadrigemina 



e. Crura cerebri. 



III. Fore-brain, prosencephalon. 



3. Thalamencephalon. 



f. Optic thalami. 



4. Telencephalon. 



g. Corpora geniculata. 

 h. Corpora striata. 



i. Cerebral hemispheres. 



THE MEDULLA OBLONGATA AND PONS. 

 STRUCTURE. 



Anatomical Structure. The medulla oblongata is continuous with 

 the spinal cord at the upper end. It lies within the cranial cavity and forms 

 the first part of the brain stem. The medulla consists of masses of nerve 

 cells situated in the interior, but pretty generally distributed throughout 

 the mass. The cell-masses are subdivided by laminae of nerve fibers into 

 groups, or nuclei, which give origin to or form the terminations of the various 

 ranks of nerve fibers. 



The nerve fibers are arranged partly in columns and partly in fasciculi 

 traversing the central cellular matter. The medulla oblongata is larger than 

 any part of the spinal cord. Its columns are pyriform, enlarging as they pro- 

 ceed toward the upper part of the brain, and are continuous with funiculi 

 of the spinal cord. Each half of the medulla, therefore, may be divided 

 into three columns or tracts of fibers, continuous with the three columns of 

 funiculi or of the spinal cord. The columns are more prominent than those 

 of the spinal cord, and are separated from each other by deeper grooves. 

 The anterior, continuous with the anterior columns of the cord, are called 

 the pyramids. The postero-median and external are represented at the 

 posterior or dorsal aspect of the cord as the fasciculus gracilis and the fascic- 

 ulus cuneatus. The posterior pyramids of the medulla, which include these 

 two columns of white matter, soon become much increased in width by the 

 addition of a new column of white matter outside the other two, which is 

 known as the fasciculus of Rolando. In the upper portion of the medulla the 

 fasciculi are replaced by the restiform bodies (the inferior peduncles of the 

 cerebellum). The lateral columns of the cord are scarcely represented as 

 such in the bulb. 



It may be said then that the bulb at its commencement differs only slightly 

 in size from the cord, with which it is continuous. It soon becomes larger 

 both laterally and antero-posteriorly. It opens out on the dorsal surface into 



