RHINENCEPHALON OF DELPHINUS 519 
The taenia semicircularis is shown in figures 12, 13, and 14, 
lying in the groove between the thalamus and the caudate nu- 
cleus, and also in figures 11 and 10 as it approaches its origin. 
Its fibers arise probably in the same region as that of the olfactory 
and parolfactory part of the taenia thalami but in these sections 
this was equally difficult to see. Its termination, the ganglion 
amygdalae, however, is well developed as illustrated in figure 9, 
section 143, which cuts its greatest expansion, and in figure 8, 
section 125. It is situated at the extremity of the lateral ventri- 
cle in the temporal lobe, and lies partly in the ventricular floor 
(fig. 8). It shows its typical appearance, several medullated 
tracts traversing it and dividing it into smaller nuclei. The 
ganglion cells did not appear to be the same size in all the com- 
partments. In section 148, figure 9, the nucleus amygdalae is 
directly continuous with the cortex of the temporal lobe, but 
more caudally (section 126, fig. 8), where the nucleus is smaller, 
there is a layer of cortical white matter forming a line of sepa- 
ration between the nucleus amygdalae and the cortex. Here it 
bulges in the floor of the lateral ventricle as it lies laterad of the 
hippocampus. 
The anterior commissure (fig. 10, section 148) is present as a 
small transverse bundle, which soon disappears when followed 
away from the midline. It is probable that of the two parts 
which usually make up the anterior commissure, only the poste- 
rior part is present, and that the anterior part connecting the 
olfactory bulbs is entirely absent. 
SUMMARY 
In the adult dolphin, the olfactory bulbs and tracts are lack- 
ing, and that portion of the mesethmoid which corresponds to 
the ecribriform plate of the ethmoid of the ordinary mammal is 
imperforate. Hence the dolphin is completely anosmatic in the 
sense of Turner’s classification. 
In addition to the lack of olfactory bulbs and tracts, the ol- 
factory cortex of the basal surface of the frontal lobe is also want- 
ing. In consequence of the recession of the cortex in this region, 
