562 



TEXT-BOOK OF EMBRYOLOGY. 



geniculate bodies proceed to the occipital region, those from the medial genicu- 

 late bodies to the temporal, and those from the ventro-lateral thalamic nuclei 

 (continuation of the medial fillet) to the future postcentral region. The 

 afferent pallial fibers are often termed the afferent or ascending projection fibers. 



Sulcus postcentrali 



Sulcus centrali 



Lobus parietal, sup. 



Region of gyrus sup- 



ramarg. and angular. 



Ramus post. 



Sulcus temper, med. 



Post, pole 

 of cerebrum 



Sulcus front, inf. 



Ramus ant. asc. 

 Fissura Sylvii 



Lobus temporalis 



Gyrus temp. sup. Gyrus temp. med. 



FIG. 487. Lateral view of the right cerebral hemisphere of a human foetus at the end 

 of the ;th month. Kollmann. 



The axones of the neuroblasts of the cortical layer grow inward, entering the 

 medullary layer. Their peripherally directed processes become the apical 

 dendrites of the pyramid cells into which most of the cortical cells differentiate. 

 According to Mall and Paton, this change of direction in the growth of the axone 

 is due to a turning of the cell axis during its outward migration. It would seem 



Sulcus orbitalis 



Insula 

 Gyrus olf. lat. - 



Gyrus semilun. 



Gyrus ambiens " 

 Pyramid " 

 Medulla 



- Sulcus olfactorius 



- Lobus olfactorius 



FIG. 488. Ventral view of the brail 

 of the sixth month. 



Post, pole of cerebrum 



of a human foetus at the beginning 

 Retzius, Kollmann. 



more probable that the cells retain an original bipolar character and that the 

 inner processes differentiate into axones instead of the cells going through a 

 monopolar stage (pp. 491 and 492 and Figs. 424 and 425). The axones of the 

 cortical cells form either efferent or descending projection fibers, proceeding to 



