36 
BULLETIN OF THE LABORATORIES 
of the perplexing problem lies in work upon the simpler types. The 
subject chosen possesses several advantages. It is a primitive repre- 
sentative of the sciuromorphs or squirrel-like rodents, having simply 
organized cerebrum and yet a greater exposed cortex than the myo- 
morphs which, at first thought, might have been preferred. The brain 
is large enough for localization experiments, but small enough for con- 
tinuous sections through at least one-half of the brain. Another inci- 
dental advantage is that the type is one whose cerebral anatomy has 
not been exhaustively treated. The resemblance in many respects is 
close to the brain of the hare, and we have data derived from the latter 
subject sufficient to serve as a guide in the present case. During the 
progress of the work the desirability of comparison with the brains of 
even lower types of structure became so obvious that resort was taken 
to the alligator and Amphibia, the results of a brief study of the former 
being embodied in a paper by one of us, in the current volume of the 
Journal of the Cincinnati Society of Natural History. A similar 
study of the brain of the opossum, being now in progress, may be 
shortly expected. 
Inasmuch, however, as the work upon the ground hog has been 
so long under way and some of the results have already been pub- 
lished, it has been thought best to present it as it now stands as intro- 
ductory to the more detailed anatomy of other rodent types. 
A word regarding the method followed may be appropriate : 
The subject chosen was the ground hog, Arctomys 7nonax^ while 
the brains of rabbits, opossums, and raccoons served for comparison. 
The functions of the cortex were investigated by electrical stimulation 
and extirpation. In this way the motor centers for the fore and hind 
legs, the muscles of the face and neck, and the sensory areas were 
accurately diagramed. A method used by us for the first time may be 
incidentally mentioned as worthy of more careful employment. As 
the electrodes were removed from the brain a small pasteboard or 
wooden peg bearing a number, was inserted and the reaction produced 
at this point was carefully recorded upon a diagram of the surface of 
the hemisphere with the corresponding number attached. After the 
removal of the brain these tags served to check the accuracy of the 
diagram, and a careful drawing was made including the areas experi- 
mented on. 
The brains were placed in chromic solution twenty- four hours and 
then in alcohol, and continuous series of sections taken in various direc- 
