THE NERVOUS SYSTEM OF MAN. 



37 



Embryonic Development of Brain.— The funda- 

 mental fact that the brain may be regarded as an inter- 

 cranial continuation of the 

 spinal cord, with swellings 

 and outgrowths atop, is 

 made evident by its em- 

 bryonic development. The 

 following figures give the 

 stages of this develop- 

 ment. In the very early 

 stages the brain is a direct 



continuation of the Spinal FlG - 21.— Diagram showing the inter- 

 lacing of dendrites of neurones. 



cord and consists of three 



hollow swellings or vesicles. These are what afterward 



become medulla (1), optic lobes (2), and thalamus (3). 



>' 



A 



Fig. 22. 



We shall call these the hindbrain, the midbrain, and the 

 forebrain (Fig. 22). The next step is the outgrowth of 

 the cerebrum (cr) and olfactory lobes (of) from the fore- 



FiG. 23. 



