86 FREDERICK TILNEY AND LUTHER F. WARREN 



nervus pinealis. He was able to trace the nerve fibers from the 

 so-called retina of the pineal eye into the stalk. Retzius 331B in 

 1895, using Golgi preparations in Ammoccetes, was able to 

 demonstrate the actual presence of nerve fibers of the pineal 

 nerve which he followed from the pineal organ to the brain. 

 This observation in similar preparations was confirmed by 

 Mayer 264 in 1897. Leydig 239 in 1896 found in Petromyzon 

 fluviatilis that nerve fibers were present only in the proximal 

 third of the stalk, while Johnston 195 in 1902 in Lampelra wilderi 

 found that the nerve fibers in the proximal portion of the stalk 

 seemed to be obliterated in some preparations. The pineal 

 nerve has a definite sheath of its own consisting of elements simi- 

 lar to those covering the brain. There is a membrana limitans 

 externa composed of neuroglia. Surrounding this is a layer of 

 pia mater and still more externally a process from the dura 

 mater. 



The central endings of the nervus pinealis have been traced 

 by Ahlborn 2 and Gaskell 145 to the posterior commissure. Gaskell 

 showed that the nerve was connected with the right habenular 

 ganglion and that this nerve structure was, therefore, the optic 

 ganglion of the pineal eye. Studnicka 388 followed some of the 

 fibers to the inner portion of the posterior commissure. He 

 thought that the pineal nerve ended in the left habenular ganglion 

 while the nerve of the parapineal organ ended in the right struc- 

 ture of this name. Mayer 264 traced the fibers by means of silver 

 impregnation to the posterior commissure. The proximal 

 portion of the pineal organ in cyclostomes is much reduced in 

 size because of the close approximation between the posterior 

 commissure and the commissura habenularis. A small recess, 

 however, marks the position of the proximal portion in these 

 forms and is situated between the two commissures just men- 

 tioned. This is the recessus pinealis. The pineal organ in 

 cyclostomes has been called the epiphysis, the epiphysis cerebri, 

 and the superior vesicle of the epiphysis, according to Ahlborn 

 in 1883.* 



The parapineal organ in cyclostomes. The more cephalic of 

 the two epiphyseal elements in cyclostomes has been called by 



