MEDIAN EYES 



715 



Fig. 860. — The Parietal akd Pineal Bodies of SpHESoDoy pvsctatvs. 



A lateral view of the brain. C, cerebellum ; O, optic lobe ; OL, olfactory lobe ; 

 ON , optic nerves ; Par, parietal eye ; Pin, pineal body (epiphysis) ; IV, fourth ven- 

 tricle. The structures issuing below are the cranial nerves, III to XII. 



degenerates and disappears in adolescence leaving a rudiment of an eye 

 connected by a nerve with the posterior commissure (Fig. 858) (Leydig, 

 1891 : Braem. 1898 ; and others). 



In the primitive reptiles the eye-structure reaches its highest develop- 

 ment in the parietal organ (Figs. 859-860) ; in the New Zealand tuatara 

 [Sphenodon). for example, it passes through the skull by a " parietal foramen" 

 and lies beneath the skin, the scales of which become specialized and 

 transparent in this region. In this animal as well as in some other types, an 

 ACCESSORY PARIETAL ORGAX lies coutiguoush' ; it is variable in structure, 

 vesicular or sohd. and tends to disappear with maturity. In lizards such as 

 Lacerta, the arboreal lizard. Iguana, and the slow-worm, Ancjuis (a limbless 

 lizard), the parietal eye loses connection entirely with the pineal body and 



Fig. 861.- 



-The Pineal Gland in Man (from Gladstone and ^Vakeley, Tht 

 Pineal Organ). 



