THE NERVOUS SYSTEM. 



525 



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 postcentralis 



Sulcus centralis 



Lobus parietal, sup. 



Region of gyrus sup- 



ramarg. and angular 



Ramus post. 



Sulcus tempor. med. 



Post, pole 

 of cerebrum 



Sulcus front, inf. 



Ramus ant. asc. 

 Fissura Sylvii 



Lobus temporalis 



Gyrus temp. sup. Gyrus temp. med. 



FIG. 449. Lateral view of the right cerebral hemisphere of a human foetus at the end 

 of the yth 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 



Post, pole of cerebrum 



FIG. 450. Ventral view of the brain of a human foetus at the beginning 

 of the sixth month. 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. 454 and 455 and Fi s - 3^6 and 387). The axones of the 

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



