22 FREDERICK TILNEY AND LUTHER F. WARREN 



with the pineal organ, the so-called pineal nerve, ends in the 

 posterior commissure, while the parapineal nerve has its termi- 

 nation in the commissura habenularis. 



Probably the first observation upon this region in the cyclo- 

 stomes was made by Serres 353 in 1825. Other contributions fol- 

 lowed by Schlemm and d'Alton 347C in 1838. Johannas Miiller 280 

 in 1838 and Siebold and Stannius 355 in 1854 added their studies 

 of this region. Mayer 265 in 1864 mentioned the occurrence of 



Epid Cor 



-.Sohd 



JLs 



Fig. 1 Schematization of pineal region in Cyclostomes, according to Stud- 

 nicka, 1905. 



Ls., lamina terminalis ; .P/, paraphysis; Pp., parapineal organ ',Po., pineal organ; 

 Ha., habenular ganglion; Th., parapineal nerve; Ch., commissura habenularis; R., 

 recessus pinealis; Cp., commissura posterior; n., Npin., nervus pinealis. 



many calcium corpuscles in and about the pineal organ. Wie- 

 dersheim 422 in 1880 spoke of the epiphysis as a small, saccular 

 body, but it was not until 1883 that Ahlborn 2 first described the 

 microscopic appearances of the epiphyseal complex in which 

 he was able to observe two superposed vesicles. Ahlborn, 

 however, did not interpret these two vesicles as independent 

 evaginations from the roof of the interbrain, but considered 

 them as subdivisions of the epiphysis. 



