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FREDERICK TILNEY AND LUTHER F. WARREN 



and plexiform, in many forms attaining a marked vascularity. 

 The next structure in the pineal region is the commissura habenu- 

 laris, following which is a long pars intercalaris anterior. Then 

 follows the epiphysis or the proximal portion of the pineal organ 

 with a marked pineal recess. There can be little doubt that 

 this particular form in which the pineal organ presents itself 

 is the actual proximal part of other species. Following the 

 epiphysis is a thick pars intercalaris posterior, and finally the 

 posterior commissure. 



Npin 



Fig. 4 Schematization of the pineal region in Amphibia, according to Stud- 

 nicka, 1905. 



Ls., lamina terminalis; Pf., paraphysis; Ds., dorsal sac; Ch., commissura ha- 

 benularis; Po., pineal organ; Npin, nervus pinealis; Ep., proximal portion pineal 

 organ; Tp., tractus pinealis; Sch., pars intercalaris posterior; Cp., commissura 

 posterior; M., midbrain. 



7. The pineal region in reptiia 



In Prosaurians and Saurians, as in Petromyzon and some 

 teleosts, both the pineal and parapineal organs make their appear- 

 ance, but the order which they hold in the lower forms is some- 

 what reversed here since the parapineal organ gives rise to an 

 eye-like structure called the parietal eye. This parietal eye, 

 however, is present only in the lower reptiles. The pineal organ, 



