RHINENCEPHALON OF DELPHINUS 505 
with the regio olfactoria, and perhaps some with the nucleus of 
the fifth nerve. Bindewald (713) studying this region in the 
elephant, found it very large as one might expect in an animal 
with such a large and sensitive snout apparatus as the trunk. 
Thus there is no final agreement as to its status at the present 
time. 
“ The planum septale, or anterior perforated space of human 
anatomy, is a region where normally the central ganglia come 
to the surface without any cortical covering. In the dolphin 
(fig. 4) we will see that there is a much increased area of central 
ganglion exposed. 
The extent of the lobus pyriformis varies greatly in different 
orders, but in all it is a palaeencephalic structure. In lower 
mammals it comprises the entire region mesial to the fovea 
limbica or rhinal fissure, but in higher mammals neopallial 
structures also develop in this area. In this view of the adult. 
human brain (fig. 3), practically nothing is seen of the much 
diminished lobus pyriformis within the vallecula Sylvu, but in 
the 5-month fetus brain it is easily recognizable as an acutely 
bent band running laterad of the planum septale, and ending 
caudally in the temporal lobe (see Villiger-Piersol, 1912, p. 26, 
fig. 26). In the adult this caudal portion becomes fused with 
part of the temporal lobe, although the diminutive gyri semi- 
lunaris and ambiens still show as landmarks indicating its limit, 
and the slight'incisura temporalis at the margin of the uncus 
persists as the representative of the primitive rhinal fissure. 
EXTERNAL FORM OF DOLPHIN BRAIN 
The cetacean brain is wide and blunt, and presents an appear- 
ance quite different in some respects from that of all other mam- 
mals (figs. 4 and 6). The frontal part does not taper towards 
the nose, but curves round in a strange way, so that what is 
usually the most frontal point has to be looked for at the base of 
the brain, not far frontad of the chiasma. Thus the whole organ 
is not egg-like in form but is more globular, and it is quite possible 
that this shape is the result of the retrogression of its olfactory 
