192 RALPH EDWARD SHELDON 
ventrally, close to the median cavity, while the other remains 
dorsal, meeting the lateral olfactory area in the polus posterior 
of the hemisphere, and then continuing caudally under the haben- 
ula. This forking column of cells is, as will be brought out more 
clearly later, the morphological equivalent of the precommissural 
body or paraterminal body of Elliot Smith in mammals and rep- 
tiles, and is, therefore, here termed the corpus precommissurale. 
The rostral portion of the nucleus corresponds morphologically 
to the rostral part of the ganglion mediale septi of Gaupp, or the 
area precommissuralis septi of Kappers and Theunissen in the 
frog, and is called, therefore the nucleus medianus (fig. 25). 
The portion of the nucleus extending into the commissure is 
simply the bed of the anterior commissure of Elliot Smith in 
reptiles and mammals and is called, therefore, the pars commis- 
suralis. The arm of the precommissural body arching over the 
commissure presents points of resemblance to the pars fimbrialis 
septi of Kappers and Theunissen in the frog. It is here called the 
pars supracommissuralis (figs. 35, 36, 38, 55, 56, 61). Its exten- 
sion caudad behind the commissure joining the lateral olfactory 
area is named the pars intermedia (figs. 66,67, 68, 70). Thecom- 
missure bed passes immediately caudad into a nucleus of small 
cells, bordering the ventricle, which is here termed the nucleus 
preopticus (figs. 61, 66, 67, 68, 70, 73, 76, etc.). This is composed 
of several different cell groups which will be taken up in greater 
detail later. 
All parts of the corpus precommissurale appear very discrete 
in toluidin blue preparations. In the nucleus medianus, the 
cells are closely packed, but are arranged in groups or islands 
(figs. 25, 26). (See Calleja, 93.) Usually a clear zone of few 
cells surrounds the precommissural body particularly dorsally 
and laterally (fig. 38). In the pars supracommissuralis the cells 
are less closely packed (figs. 38, 46, 56), and have lost the island 
arrangement. The grouping in the pars commissuralis, is largely 
dependent on the position of the fiber bundles of the anterior com- 
missure; the cells are, however, fairly evenly distributed (figs. 
38, 56). 
