I20 Journal of Comparative Neurology. 



nidulus lies cephalo-mesad to the lenticular nidulus, and is 

 separated from it by a narrow band of nerve fibres. This is 

 the largest nidulus in either the mesencephalon or tlie dien- 

 cephalon. It extends from the lenticular nidulus almost to 

 the union of the mesencephalon and diencephalon. Being 

 widest at its contact with the nidulus lenticularis, it tapers 

 gradually from that nidulus to its extremity. In shape this 

 cell cluster is not a perfect pear, the symmetry being de- 

 stroyed by the lenticular nidulus, which rests upon the 

 obliquely truncated caudo-laterad extremity of this nidulus. 

 Histology. — The cells of this nidulus are numerous, and 

 are arranged parallel to its longitudinal axis. This arrange- 

 ment makes the cells of the lenticular nidulus perpendicular 

 to the cells of the pyriform nidulus. These cells bear no 

 resemblance whatever to those of the lenticular nidulus. 

 They are much smaller and of an entirely difierent type. In 

 the blue bird [Stalia sialis) these cells are about ten micro- 

 millimetres long and five micro-millimetres broad. They are 

 fusiform in outline, thus contrasting strongly with the pyra- 

 midal cells of the neighboring nidulus. In htematoxylin and 

 in aluminium-sulphate cochineal preparations, each cell is 

 faintly stained, and presents a clear sub-spherical nucleus 

 and a dense nucleolus (Plate XVI, Fig. i). This cell cluster 

 is amply supplied with Deiter's corpuscles, and is surrounded 

 by fibre tracts. 



Corpus postcrhis (Plate XV, Figs. 5, 8). — In the caudo- 

 laterad portion of the diencephalon, at the junction of that 

 portion of the brain and the mesencephalon, there is a small 

 but well-defined nidulus. This cell cluster has received 

 several names. In 1SS9 Dr. Perlia(') named it the " nidulus 

 of the median optic fasciculus" (Kern des median optic 

 Biindle). In the previous year Bellonci(') christened it 

 " corpus posterius." This nidulus varies in shape from a 



1 •' Ueber ein neues Opticus centrum beim Huhne." Von Ur. Perlia. Albrecht 

 von Graefe's Archiv f. Ophthalmologie, Bd. XXXV, taf. ii, Fig. 5. 



2 Op. cit., p, 16, Fig. iii, Kcp. 



