18 Comparative Neurology. [ January, 
auditory sense derived from the general tactile or a special touch 
sense (like that of the fifth pair of nerves). An optic sense would 
arise from this same tactile, and we have seen it thus differentiated 
embryologically. 
Qualitative differentiation of the nervous organization proceeds 
dorsally, with a tendency toward the head end. That portion of 
the animal which stands in most direct relation to the changing 
molecular movements of the environment develops the highest 
sensory and motor nerve-centers and projections. 
Repetition of parts of a system, up to a certain point ceases ; and 
these parts become commissurally united before another system 1s 
perfected. 
The sympathetic nervous system, consisting of the intestinal a 
and vascular or vaso-motor nerves, develops first. Blending the 
results of comparative embryology and anatomy, the yas 4 
precedes the creation of other systems. 
The second system to appear phylogenetically is the spinal, 
equivalent in the Invertebrates to their “cerebral” ganglia. 
The third system is the intervertebral, the swellings upon the 
posterior roots of the spinal nerves. 
The cerebellum is formed from fused hypertrophied intervertebral 
ganglia. 
Many sensory cranial nerves pass through this organ and by 4 
the fusion of these originally separate centers codrdination occurs 
necessarily. 
Excessive development on the one hand, or want of develop- 
ment on the other, places all the ganglionary tubercles and lobes ~ 
of the encephalon in the third system category. Thus the pr@- — 
frontal lobe of the cerebrum, the occipital and temporal lobes, the — 
olivary body, the olfactory lobe, the mammillary eminence, the 
epiphisis cerebri, the tubercula bigemina, the petrosal and Gassertan q 
ganglia were originally intervertebral ganglia, and still maintain — 
resemblance to these ganglia in many particulars. 
The pre-frontal lobe is the last intervertebral ganglion to develop. : 
It grows larger in the scale of intelligence and presses the occi- : 
pital (see the brains of monotremes and marsupials) backward, 
downward and forward, thus forming the temporal (or what has 
been erroneously termed the middle) lobe. 
The cerebro-spinal nerves, in some cases, preserve their original 
projections from and to muscles, but these nerves may also have — 
