44 



CHARLES R. ESSICK 



Fig. 9 Oblique section through the rhombencephalon of an 80 mm. 

 X 7.5 (No. 172, si. 200, sect. 2). 



fetus. 



but furnishes a beautiful single section which includes all of the 

 relations of the cells wandering to the pontine nuclei. Owing to 

 the cervical flexure a cut which sections the spinal cord trans- 

 versely passes tangentially through the medulla and pons (fig. 

 9). The great thickness at which these sections were cut gives 

 the migrating column of nuclei a very deep red stain, almost 

 black, and I have represented it as black ; the plane of section falls 

 behind the roof thickening which marks the true germinal centers, 

 but it does show with remarkable clearness the whole path of the 

 neuroblasts starting from the ventricular edge, encircling the 

 corpus restiforme, passing between the facial and acoustic nerves, 

 to take their place among the cross fibers of the pons. 



During the period extending through fetus 508 (143 mm.) 

 there is a continued addition of cells to the basilar part of the pons. 

 In a fetus of the thirteenth week, 96 mm. (No. 484), the maximum 

 production of new cells has been reached. At this time the ven- 

 tricular edges on both sides of the brain are full of karyokinetic 

 figures and extending from these places are two thick columns of 



