228 



THE PINEAL ORGAN 



(Fig. 161). The end vesicle, however, soon becomes cut off from the 

 stalk by the ingrowth of the roof of the skull (Fig. 162), and the stalk 

 disappears leaving only the proximal part or epiphysis in connection with 

 the roof of the diencephalon. 



The end vesicle, or parietal organ (Fig. 167, p. 233), is situated beneath 

 the epidermis, being imbedded in the corium and lying completely outside 

 the roof of the skull. Its position in the living animal is indicated by 

 a small, pale area, the parietal spot where the pigment in the sub-epithelial 



Fig. 161. — The Parietal Region and Pineal Organ of a Tadpole (Rana 

 temporaria) — Internal Gills and Hind Limbs appearing as Stumps. 

 (After Braem, 1898.) 



Ch. H. : chiasma habenularis. 



Ch. p. : chiasma posterior. 



Ds. : dorsal sac. 



Ep. : epiphysis. 



L. Sn. : lamina supra-neuroporica. 



MB. : midbrain. 



N. pin. : nervus pinealis or stalk of 



pineal organ. 

 Par. : paraphysis. 

 Po. : pineal organ. 

 V. : velum. 



Fig. 162. 



Median longitudinal section of the pineal diverticulum of a frog tadpole, showing a 

 constriction in the plane of the cranial capsule, which indicates the future line 

 of separation of the parietal organ (Stieda) from the epiphysis or pineal sac. 

 The apex of the organ is directed forward, and is to the right in the figure. 



(Original R. J. G.) 



C. : constriction; Epd. : epidermis; Op. P. St. : opening of pineal stalk ; 



St. O. (Pa. O.) : parietal organ (Stieda; ; V. III. : third ventricle. 



