3io 



THE PINEAL ORGAN 



diencephalon and midbrain, the thin lower part of the interhemispheric 

 septum disappears (Fig. 215, S.), while the thick upper part persists as 



G.C.V. 



CJV.V 



C.N. Ill 



C.N. IV 

 T. Cbl. 



Fig. 215. — Transverse Section through the Posterior Thalamic Region of 

 a 6-cm. Human Embryo in Front of the Pineal Organ, showing the 

 Relation of the Cerebral Membranes to the Great Cerebral Vein and 

 Neural Tube at the Junction of the Lateral Plate with the Dorsal 

 Lamina, and the Extreme Thinness of the Membrane (Lower Part of 

 Interhemispheric Septum) which joins the Sheath of the Great Cerebral 

 Vein to the Lower Margin of the Falx Cerebri. (R. J. G.) 



C.H. : cerebral hemisphere. 

 Ch. P. : choroid plexus. 

 C.N., III., IV., V. : cranial nerves. 

 I.S.S. : inferior sagittal sinus. 

 G.C.V. : great cerebral vein. 

 M.B. : bundle of Meynert. 



O.T. : optic thalamus. 



P.M., P.M. 1 , P.M. 2 : pia mater. 



5. : septum interhemisphericum (falx 



cerebri). 

 T. Cbl. : tentorium cerebelli. 



the definitive falx cerebri, the inferior sagittal sinus (Fig. 215, I.S.S.) 

 being developed in its lower border. The septum in the earlier stages of 

 development is very much thicker than at the stage described, and is 



