THE AMYGDALA IN AMPHIBIA 250 
The dorsolateral quadrant of the amphibian hemisphere is 
also a derivative of the primitive lateral olfactory nucleus. In 
urodeles it is scarcely more than this; in anurans it has assumed 
more of the characteristics of the mammalian pyriform lobe, but 
even in mammals this area has deviated far less from the most 
primitive condition (viz., lateral olfactory nucleus) than has the 
corpus striatum. 
The distinctive characteristics of the differentiated corpus 
striatum of higher forms include neither olfactory nor hypothala- 
mic connections. Its predominant functional relations are 
rather with diencephalic sensorimotor systems termed by many 
recent writers somatic, viz., the somesthetic complex and perhaps 
the optic and auditory reflex systems. Its chief fiber connec- 
tions are with the thalamus proper (pars dorsalis thalami, as I 
defined that term in 1910) on the afferent side and with the 
motor tegmentum of the thalamus and midbrain on the efferent 
side. 
The corpus striatum complex, however, makes its appearance 
in lower vertebrates within the lateral olfactory area, and there 
is evidence that, as its phylogenetic differentiation progressed 
under the influence of increasing numbers of ascending thalamic 
fibers, the receptive apparatus of the thalamic tracts and the 
related motor neurons discharging into the tegmentum segre- 
gated away from the apparatus receiving the descending second- 
ary olfactory fibers, thus forming the true striatum. 
The lateral olfactory area, moreover, in all vertebrates has an 
important hypothalamic connection comprising both ascending 
and descending fibers, the tractus pallii of fishes and the olfactory 
projection tract of mammals. And this hypothalamic connec- 
tion, unlike the thalamic apparatus, maintains throughout the 
veretebrate series its physiological relationship with the lateral 
olfactory centers. 
The following physiological factors, accordingly, must be 
recognized as influencing the morphogenesis of the lateral wall 
of the vertebrate cerebral hemisphere: 
1. The primary influence of the lateral olfactory tract. 
