130 Journal of Comparative Neurology. 



epithelium or radial superficial layer of cells with entally directed 

 processes. 



The geniculatum (Fig. 3, Plate XVI, gen.) lies dorsad of 

 the ventral peduncles and receives fibres from the dorsal pedun- 

 cle which are less compact than those of the ventral. Caudad 

 of the level where the geniculatum occupies the surface a scat- 

 tered infra-habena nidulus appears dorsad of the subthalamicus. 



The infrahabenaria and Meynerts' nidulus are separable 

 from the habena proper. The respective positions may be 

 gathered from Plate XVI, Fig. 3, and the figures on Plate 

 XVII. 



The nidulus nibcr has hitherto not been identified in am- 

 phibians. Reissner figures the bundles of the commissura hori- 

 zontalis^ and indicated them as " herabsteigende Biindeln von 

 Nervenfasern, " the figure is from a section somewhat too far 

 cephalad to show the nidulus very well — its real site is in 

 the most protuberant region dorsad and laterad of C in the fig- 

 ure. The structure of the nidulus is less close than in the fishes 

 but it is obviously like the latter, a terminus of many of the 

 dorsal peduncular fibres. Under a high power the cells resolve 

 themselves into those with long processes extending into axis 

 cylinders in different directions and those with less evident pro- 

 cesses lying clustered as in fishes. The whole area is filled out 

 with fibres from various directions. The recognition of this ele- 

 in the thalamus is a useful step in construing the difficult region. 

 The homology is made more complete by the fact that the tract 

 of the commissura horizontalis traverses the nidulus ventro-dor- 

 sad and leaves it on its way to the post-commissure region. In 

 the tailed amphibians I was unable to detect the ruber in 1892. 

 (Vol. II, p. 6']). (The fullest account of this nidulus yet re- 

 corded respecting fishes, etc., is that on pages 58-67 of the 

 Journal of Comparative Neurology, Vol. II.) Although there 

 is no distinct ruber in Urodela yet it is possible to trace fibres 

 of the commissura horizontalis dorsad to a point a little cephal- 



^ Bau des Centralnervensystem der ungeschwa.nzten Batrachien, Plate XII, 

 Fig. XI. 



