106 Comparative Neurology. [ February, 
The olfactory lobe (another third system ganglion) appears to 
have been derived from a place lying in front of the mammillary 
eminences, according to Luys’ sections, but Meynert is doubtless 
more correct in attaching the olfactory primitively to the optic 
thalamus. 
The olfactory lobes, of more importance in some vertebrates 
than the cerebrum, in man became strangled, so to speak, by the 
preponderance of higher third systems. 
(“ The olfactory lobe bore such important relations to the life 
history of early vertebrates that we are not surprised to find the 
cerebral hemispheres developing at first as mere appendages of the 
olfactory lobes.”—Spitzka, ‘ Architecture and Mechanism of the 
Brain,” p. 37.) 
The lobes of the cerebrum are related to the corpus striatum, 
which seems to bea part of the medullary gray second system, 
though formed after the hypophysis cerebri had become atrophic 
as the end of the spinal cord. 
The hypophysis ended in the sella turcica and the corpus stri- 
atum (caudate nucleus), and subsequently lenticular nucleus 
developed in the scale of intelligence (Meynert). 
In Teliost fishes the optic lobe (third system) occupies the 
place of the cerebrum of mammals in point of mass development, 
and the inference is natural that this optic lobe contains the 
highest centers related to the psychic life of this division of ver- 
tebrates. The cerebrum proper being an undeveloped tubercle in 
front of the mammillary eminence with the infundibulum between 
them (Todd, p. 619, Vol. 111). 
In Amphioxus we have the culmination of the secondary — 
ganglionic type with the foreshadowing, seemingly, of the tertiary, 
in the black pigmentary formation in the dorsal portion of the 
notochord. This vertebrate, so far from being anomalous, ex- 
plains by its rudimentary organization what appears later in the 
Cyclostomi or above. Its second pair of nerves runs from the 
dorsal segmental nerves to the head-end ganglion, thence to the 
ventral segmental nerves, typifying the medulla oblongata control 
over lower centers, without the intervention of a cerebellar or any 
other third system. 
The optic ganglion (secondary) of the crab ( Carcinus muenas) 
topographically precedes the antennal, from which may be inferred 
that the posterior bigeminal (tertiary) is related, as ear claims, 
to the special tactile (fifth pair) sense. 
