THE NERVOUS SYSTEM 





the brain and spinal cord is known as the cervical flexure (Fig. 16). From 

 the walls of the prosencephalon there develop outpocketings on either side, 

 which form the optic cups and which are connected to the brain by the optic 

 stalks. From the cup develops the retina and through the stalk grow the 

 fibers of the optic nerve. These structures are, therefore, genetically parts of 

 the brain. 



The Telencephalon of the Human Embryo. By the time the embryo has 

 reached a length of 13 mm. the brain has passed into the stage represented by 



Mesencephalon 



Rhombenccphalon 

 Myelencephalon 



Amnion (cut) 



Mesodermal segment 14 

 Open neural groove 



Body stalk 

 Fig. 14. Human embryo of 2.4 mm. showing the neural tube partially closed. (Kollmann.) 



diagrams E, F, G of Fig. 7. The lateral wall of the telencephalon, with the 

 corpus striatum and olfactory brain or rhinencephalon, has been evaginated on 

 either side to form paired structures, the cerebral hemispheres (Fig. 16). Ex- 

 cept for the corpus striatum and rhinencephalon the evaginated wall is relatively 

 thin, develops into the cerebral cortex, and is known as the pallium. The 

 lateral ventricles within the hemispheres represent portions of the original telen- 

 cephalic cavity and communicate with the third ventricle through the inter- 



