No. I.] AMPHIBIAN BRAIN STUDIES. 53 
gray matter of the brain immediately surrounds the ventricles, 
the central gray, and with the exception of the layers of cells 
in the optic lobes of the Azwura, there is nothing developed in 
the nature of the cortical gray matter. The Uvode/a are further 
distinguished from the Azura by the small size of the optic 
lobes, which are barely marked off from the thalami, by the 
frequently extensive development of the superior commissure, 
and by the primitive condition of the ventriculus communis or 
unpaired cavity of the prosencephalon. 
I. THE DIVISIONS AND CAVITIES OF THE ADULT BRAIN. 
The division of the brain into five large segments is invaria- 
bly well marked. The olfactory lobes do not appear as fully 
distinct segments, but form the anterior portion of the prosen- 
cephalon, sometimes separated from the hemispheres by a 
prominent lateral swelling or median indentation. The line of 
separation is much more clearly indicated in horizontal sections. 
The olfactory nerves arise either from the edge or base of the 
lobes. The lobes are broad and truncate anteriorly in the Uvo- 
dela,! but taper in Proteus as in the Frog. The diencepha- 
lon and mesencephalon are subequal in size in the genera 
with small functional eyes, such as Szvedon, Necturus, and Stren, 
these two segments presenting the appearance of an elongate 
cylinder slightly compressed opposite the posterior commissure. 
In the blind Proteus the mesencephalon is smaller than the 
' The classification adopted is from Baur’s valuable memoir, “ Beitrage zur Mor- 
phogenie des Carpus und Tarsus der Vertebraten, I Theil, Batrachia,” Jena, 1888. 
The recent Amphibia are arranged in three orders : — 
PROTEIDA. URODELA. ANURA. 
Fam. Proteide. Proteus. Fam. Cryptobranchide, Cryptobranchus. 
Necturus. Sirenide, Siren. 
Pseudobranchus. 
Amphiumide, Amphiuma. 
Amblystomatine, Amblystoma 
(Axolotl), etc. 
Also the Cecilitde, Plethodontide. 
Desmognathide,  Salamandride. 
Pleurodelide. 
Baur considers the Cryftobranchid@ the most central family of the Urodela, from 
which the Strentde, Amphiumide, and Amblystomide may have sprung, p. 55. I 
find that the brain structure fully supports this conclusion. 
