302 JOURNAL OF COMPARATIVE NEUROLOGY. 
central terminal relations, and functionally by the trasmission of 
nervous impulses of the same type or modality. Among these 
systems are tactile, auditory, visual, olfactory, motor, gusta- 
tory, etc., each with very characteristic terminal relations. 
Now, this structure is absolutely meaningless apart from 
its function. Let any one who doubts this spend a few months. 
(as I have done) in trying to master and correlate the existing 
literature of the cranial nerves of vertebrates. Though these 
descriptions were for the most part written by famous masters 
of anatomical science, yet in their aggregate they present an 
indigestible mass of confused and meaningless detail, crude fact, 
well spiced with error, for the most part not worth the prodig- 
eous labor of digging it out of the oblivion of classic tomes of 
by-gone anatomists. 
I do not mean to imply that all the problems of cranial 
nerve morphology are now cleared up; but I do claim that 
there is no longer any necessity for the further accumulation of 
uncritical and meaningless fact in this field of research. We 
have already gone far enough to point the way toward certain) 
lines of fruitful correlation. We can not only correlate structure 
with structure, but we can interpret structure by function and. 
thus bring out a fuller meaning. We are at least coming into a 
realization of the fact that we cannot fully understand any struc- 
ture until we know what it can do. 
This point of view of course is not new, but as worked out 
practically in the peripheral nervous system it is exerting a 
clarifying influence upon our knowledge of the central system 
also. The present demand in cerebral anatomy is for conduc- 
tion paths, for functional systems of neurones, and precise 
knowledge of the pathways between the brain and the periphery 
is the first step in such a central analysis. 
The primary function of the nervous system is to facilitate 
the reaction of the organism to the external forces of the environ- 
ment. Later, as the reacting mechanism becomes more com- 
plicated, the nervous system assumes the function of coordi- 
nating this mechanism, i. e., of reaction to the forces of the 
internal environment. These two functions lie at the basis of 
