376 



ELEMENTAR Y ANA TOMY. 



[LESS. 



fact it is in the middle of the complex whole of the adult 

 structures. 



c. 



P t 



FIG. 330. DIAGRAM ILLUSTRATING THE PROGRESSIVE CHANGES THAT TAK.S 

 PLACE DURING SUCCESSIVE STAGES OF THE DEVELOPMENT OV THE BRAIN. 



i. The brain in its very early condition, when it consists of three hollow vesicles, 

 the cavity of which is continuous with the wide cavity (ti) of the primitive 

 spinal marrow (m). The brain substance forms an envelope of nearly equal 

 thickness throughout. 



a. Here the first vesicle or fore-brain has developed the pineal gland (//) above 



