84 K. S. LASHLEY AND S. I. FRANZ 



some evidence of the retention of the habit. An exact estima- 

 tion of the individual degree of retention is precluded by the 

 Simplicity of the habit and the different extents to which the 

 animals showed shock effects of the operation. Since all the 

 animals with lesions restricted to the frontal regions retained 

 the habit wholly or in part and since the lesions were for the 

 most part incomplete the first question that arises is whether or 

 not any particular area in the frontal region was left intact in 

 all the animals. The combined extents of the lesions in this 

 series are shown in figure 2. The entire frontal pole of each 

 hemisphere extending down to the olfactory tracts was destroyed 

 in one or another of the animals. No one part of the frontal pole 

 remained undestroyed in all. It seems, then, that no particular 

 part of the frontal pole of the rat's cortex is necessary for the 



FIG. 2. TOTAL EXTENT OF INJURIES TO CORTEX IN ANIMALS DESCRIBED IN 



SERIES I 



All parts of the cortex anterior to the knee of the corpus callosum have been 

 destroyed. 



retention of the maze-habit; there is no specialized region con- 

 cerned with the maze-habit which has a uniform position for all 

 animals. Furthermore, in some of the animals (experiments 

 1, 3, 4, 10 and 11), there was an almost complete destruction of 

 all the cortex above and in front of the knee of the corpus callo- 

 sum so that it seems very probable that no part of the frontal 

 region of the rat's brain is concerned with the retention of the 

 maze-habit. 



A number of attempts have been made to find some correla- 

 tion between the extent of lesion in these cases and the accuracy 

 of performance in the retention tests but no such correlation 

 seems to exist. Both animals with extensive and those with 

 slight lesions made perfect records in the retention tests 



