46 CHARLES R. ESSICK 



further development of the pons consists of an addition of axones 

 (with their later myelinization) and the maturity of the nerve 

 "cells. The rhombic lip has given up all signs of activity in the 

 next stage of which I had access to serial sections. In No. 509 

 (188 mm.) the lining of the central canal is uniformly at rest in 

 the medullary region and is now as sharply demarcated around 

 the roof attachment as that covering the basal and alar plates. 

 The roof thickening now reminds one of those sections through the 

 adult medulla which pass through the ponticulus of Henle. Com- 

 paratively few of the cells have not descended into the pontine 

 region but are taking on the characters of adult ganglion cells 

 along the path where the pontine cells migrated at an earlier period. 

 Just how many cells fail to move into the pontine region but take 

 up their position around the restiform body varies in the differ- 

 ent brains. This helps us to understand the wide differences 

 which were noted in the size of the fully developed corpus ponto- 

 bulbar. With the disappearance of the closely packed nuclei 

 around the attachment of the rhombic lip and the consequent 

 clearing up of the roof thickening, the ventricular outpouchings 

 stand out with great clearness. They are not very unlike tubular 

 glands with a single cell lining them and show a tendency to 

 branch frequently. 



The increase in the number and size of the bundles of cross 

 fibers in the pons gives the basilar part a greater thickness in 

 the adult where one finds the fiber material outweighing the 

 nuclear material. In the first beginnings on the contrary just the 

 reverse holds true, and the nuclei pontis alone form the protu- 

 berances in the pontine region. The individual ganglion cells, 

 although larger than the preceding stages, are still immature. 

 The protoplasmic bodies do not accept the counter stain and few 

 of the nuclei possess a well formed nucleolus. 



By the eighth month (No. 491) the protoplasm of the ganglionic 

 cell is no longer clear but takes up the counter stain. Many of 

 them now look like the ganglion cells of the adult except for their 

 smaller size. The entire migratory path is strewn with cells. 

 Passing between the facial and acoustic nerves the column can be 

 traced around the restiform body into the roof of the fourth ven- 



