THE AMYGDALA IN AMPHIBIA 1 207 
hypothalamus, where its further connections are unknown. In 
lower Amphibia a similar condition was described (Herrick, 
17, p. 248), but the fibers could be traced forward only as far 
as the level of the III nerve. They probably reach the hypothal- 
amus.” 
It is not improbable that there is a direct or indirect connection’ 
between the tertiary ascending gustatory system just mentioned 
and the hypothalamic nucleus of the olfactory projection tract, 
thus putting the gustatory system into physiological relationship 
with the olfactory centers of the lateral wall of the cerebral 
hemisphere. This latter connection is very primitive.® 
Now in the Amphibia the opening of the internal nasal passage 
(choana) introduced a new functional factor into the peripheral 
olfactory complex, viz., the reception of odorous emanations from 
the mouth cavity. The central correlation of these newly 
acquired excitations with those received from taste buds in the 
course of the feeding reactions naturally accompanied this change 
in peripheral relations, the mechanism for this being already 
present in generalized form in the broad connection between 
the lateral olfactory area and the hypothalamus by way of the 
olfactory projection tract. This is the condition in urodeles. 
With the appearance of a vomeronasal organ in definitive form 
2In the passage cited (’17, p. 249) I referred to the secondary visceral (and 
gustatory) nucleus as belonging ‘‘in the midbrain, rather than in the medulla 
oblongata.’’ This statement requires correction; for in view of the fact that the 
nucleus in question lies behind the sulcus isthmi (as described on page 222 of the 
same paper), it must be regarded as rhombencephalic if the sulcus isthmi is 
correctly interpreted as marking the rostral boundary of the rhombencephalon. 
The corresponding region in teleosts (Uebergangsganglion) has been shown to 
be rhombencephalic by Palmgren (Acta Zoologica, vol. 2, 1921, p. 91). 
’Dart (’20, p. 17) has asserted that the olfactory projection tract (tractus 
pallii) ‘‘is the only ascending tract from the hypothalamus,”’ and that there are 
no ascending fibers from this region in the medial forebrain bundle. In this he 
ignores or rejects a considerable body of positive observation, some of it based 
on ample material stained by the Golgi method, published by competent ob- 
servers. From the study of my own preparations I have no doubt that there are 
such ascending fibers in the medial forebrain bundle. The medial wall of the 
cerebral hemisphere must, accordingly, be recognized as sharing with the lateral 
wall in the reception of ascending hypothalamic tracts. The broad functional 
differences between these regions must be interpreted in terms of other factors. 
