24 Journal of Comparative Neurology. 



Rabl-Ruckhard (72-78) in his interesting paper on the 

 Central Nervous System of Alligators gives the following 

 description of the roof of the diencephalon : Posteriorly 

 the roof is limited by the post-commissure and the elongated 

 round conarium. The roof of the third ventricle is entirely 

 membranous. As a transverse section shows, the vascular 

 plexus of the roof proceeds over the dorsal limb of the optic 

 lobes in a dorso-median direction to unite with an arch-like roof 

 which lacks the ependyma and its highly developed plexus chor- 

 oideus. In a longitudinal section we see that the roof of the 

 corpora quadrigemina is somewhat thickened anteriorly. Join- 

 ing this is a thin limiting membrane hardly as thick as the velum 

 medullare anterius. This projects anteriorly and slightly dor- 

 sally and ends apparently in a knob-like thickening. This form 

 in the longitudinal section arises from a transversely placed edge 

 which bends around at right angles on both sides toward the 

 front. The transverse section shows that the tela choroidea su- 

 perior is attached to these edges throughout their entire length, 

 while on the posterior part the conarium enclosed by these three 

 edges lies in the groove which is open in front. This formation 

 is thus properly designated as the taenia medullaris conarii. 

 Whether the posterior transverse part is homologous with the 

 peduncle conarii, he was not able to decide, as he could not de- 

 termine the union of the conarium with it. Within, on the two 

 posterior edges of the groove which are separated from one 

 another only by the narrow fissure of the third ventricle, lies a 

 tiny flat projection which is recognizable in spite of its diminu- 

 tive size. A transverse section shows an elevation of the groove 

 over the surface of the optic lobes and a corresponding arch in 

 the projection. Rabl-Rikkhard in his article (j2-%$) gives the 

 following summary : The pineal gland appears very diversely de- 

 veloped in the different families of fishes. In the salmon it has 

 become a large gland-like funnel of the form of an elongated 

 pear, whose narrowed stalk arises immediately in front of the 

 anterior commissure, while the body (of the pineal) lies far in 

 front on the rudimentary mantle of the fore-brain and buried in 

 a groove of the frontal cartilage. There is an opening between 



