406 J. B. JOHNSTON 
scattered between the islands. Some of the cells in the islands 
take a lighter, more transparent and brilliant stain in neutral 
red than others. 
In addition to the islands of large cells there are a number of 
dense clusters of small cells which are undoubtedly nerve cells. 
These clusters do not present a core or lumen and the neuropile 
does not shrink away leaving a clear space around them as hap- 
pens in the case of the vesicles described in the caudate nucleus. 
The true islands are confined to the deeper layer of the tuber- 
culum. It must be noted, however, that the tuberculum extends 
into the medial wall and merges with the medial parolfactory 
nucleus. The distribution of the islands may arbitrarily be taken 
as determining the extent of the tuberculum. The greater 
number of islands is found near the mediobasal angle and they 
do not extend far laterally. Caudally the islands disappear 
from the basal surface where the medial forebrain bundle collects 
(fig. 24) and are found farther caudad in the medial wall. 
There is a very close resemblance between the tuberculum 
- olfactorium in the turtle and the ‘superficial basal area’ described . 
by the writer in selachians (1911). The writer was unwilling 
at that time to give the name tuberculum olfactorium to this 
area because it seemed to include parts of the medial and lateral 
olfactory nuclei and the region corresponding to the anterior 
perforate space. The close relation of the tuberculum to medial 
and lateral olfactory nuclei is common throughout vertebrates 
and I shall present evidence at another time that the tuber- 
culum and anterior perforate space are by no means wholly 
independent. 
ANTERIOR PERFORATE SPACE 
The area corresponding to the anterior perforate space of 
mammals is not sharply marked off in the turtle. It occupies 
the caudal part of the basal surface of the large rounded promi- 
nence rostral to the optic chiasma. The rostral half of this sur- 
face shows the characteristics of the olfactory tubercle. The 
caudal half lacks these peculiarities and is largely filled by the 
medial forebrain bundle. 
