156 JouRNAL OF CoMPARATIVE NEUROLOGY. 
brates appears for the first time in the brain of the reptile. 
Both Epincer and Herrick have also shown that the first sense 
to thus enter the field of consciousness is the olfactory one. 
The pallium of the selachian really anticipates the reptilian 
olfactory connection, although, of course, in a much simpler 
way. In Mustelus, we therefore find a quite primitive condi- 
tion represented. 
So far as we may be permitted to interpret morphological 
facts, the pallium of Mustelus would appear to be a long-dis- 
tance motor centre of the olfactory apparatus. Other olfacto- 
motor centres there certainly are in abundance. Both the gen- 
eral striatum and the nucleus neuroporicus contribute motor 
neurones to the tractus strio-thalamicus; while the nucleus 
postolfactorius sends a tract to the nucleus habenulae. These 
centres obtain connection with posterior regions only through 
relays in both the interbrain and the midbrain. The pallium, 
on the other hand, sends its tract directly through the base 
of the interbrain toward the nuclei of the great nerves of the 
oblongata. The tractus pallii, therefore, gives the olfactory 
sense an additional hold on the nervous system, a series of 
connections which cannot obtain, of course, in those fishes with 
membranous pallia. 
The phylogenetic development of the pallium of selachians 
would thus appear to be the outcome of the great dependence 
which these fishes place upon the olfactory apparatus in the 
search for food. In higher vertebrates, as the olfactory sense 
becomes linked to the pallium through stronger bonds, and as ~ 
other senses make pallial connections, one after another, this 
part of the brain takes on functions of an ever higher value. In 
Mustelus, there is merely an anticipation of pallial possibilities. 
5. Supporting Elements. 
Both neurogliar and ependymal elements are present in 
the forebrain of Mustelus. 
Ependyma is found radiating from every part of the lateral _ 
ventricle, and its characters are nearly uniform for the several 
regions. The ependymal cells have their nuclei situated at 
