THE NERVOUS SYSTEM 



421 



mented retina, a more or less makeshift lens, and a well-devel- 

 oped nerve connecting the terminal organ with the brain. 

 Above this, on the surface, is situated a transparent scale, 

 surrounded by a ring of smaller opaque ones, making a con- 



FIG. 118. Lateral views of the developing human brain; drawn from 

 wax models by F. ZIEGLER after WM. His. 



The cranial nerves are indicated by roman numerals; exponent letters m and 

 s denotes respectively motor and sensory branches; e, the otic vesicle 



spicuous object on the heads of these forms. The paraphysis 

 appears to be associated with this epiphysial structure. In 

 birds and mammals there seems to be no trace of a paraphysis, 

 while the epiphysis is reduced to the form of the so-called 

 "pineal gland" pushed backwards from its original position 



