36 BULLETIN OF THE LABORATORIES 



of the perplexing j^roblem 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 w^as the ground hog, Arctoinys monax, 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 hemisi)here 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- 



