336 ELIZABETH CAROLINE CROSBY 
In his 1913 paper Johnston has discussed fully the relative 
positions and extents of the cell masses in this ventro-medial 
region of the hemisphere in cyclostomes, selachians, reptiles, and 
monotremes. Among the reptiles, he has described particu- 
larly the conditions found in the turtle. In regard to the alli- 
gator he says (13, p. 387), “In Alligator mississippiensis the 
features described above (that is the relations of the primor- 
dium hippocampi and the parolfactory area in the turtle) are 
repeated so exactly that it is unnecessary to present separate 
drawings. There are differences in general form, and the area 
parolfactoria is relatively smaller than in the turtle.” 
In the turtle Johnston has pointed out the presence of a pri- 
mordium hippocampi, ventral to the hippocampal formation. 
A similar primordium is present in the alligator and below this 
primordium and separated from it by a cell free zone and, in 
turtles, by a sulcus limitans hippocampi (Johnston, 713) is the 
area parolfactoria (in part, Herrick’s septal area). This parol- 
factory area is divided into medial and lateral portions which, 
following Johnston (715), have been termed in this account the 
medial and lateral parolfactory nuclei respectively. This area 
parolfactoria is not the lobus parolfactorius of Edinger. 
Medial parolfactory nucleus (figs. 7 to 9, 16, 17). This nu- 
cleus consists of cells of the more medial part of the parolfac- 
tory area. In the anterior end of the hemisphere it cannot be 
sharply separated from the lateral part of the area but farther 
caudad it is separated off by the fibers of the medial forebrain 
bundle. This nucleus as it is here described is practically the 
same as the medial parolfactory nucleus described for Cistudo 
carolina by Johnston (715). Medialward it is bounded by the 
nucleus of the diagonal band of Broca. 
Lateral parolfactory nucleus (figs. 7 to 9, 16,17). The lateral 
parolfactory nucleus bulges out‘into the ventricle. Ventralward 
it follows the ventricle and cannot be sharply separated from the 
nucleus accumbens, so that by some writers the whole cell mass 
has been called nucleus accumbens septi. Dorsalward this lateral 
parolfactory nucleus, in the more anterior region of the forebrain, 
is clearly marked off from the primordium hippocampi by a cell- 
