MagcuH 1, 1912] 
easiest for the anatomists to deal with, and 
it is the one to which they least often 
impute mental functions. In this connec- 
tion, however, it is of interest to examine > 
some of the evidence relating to this area 
to see how well its functions have been 
determined. In man this area is anterior 
to the fissure of Rolando, and is not simple. 
The cortex adjoining the fissure is to be 
differentiated from another anterior part 
and to these areas Campbell gives the 
names precentral and intermediate precen- 
tral. The primary part, that bordering 
upon the fissure, is the precentral, and this, 
according to Campbell, is bounded an- 
teriorly by the other zone, which is physi- 
ologically connected with it. Stimulation 
of the cortex of the precentral area pro- 
duces movements, and it has been a simple 
matter to explain the function by assuming 
that the cells govern the bodily muscu- 
lature. But movement is also produced 
when the intermediate postcentral and 
other parts of the cortex are stimulated, 
and the latter movements are the more 
complex. In the precentral cortex the 
Betz cells are those to which the motor 
function has been imputed. These cells 
differ in number and in size in different 
parts of the precentral cortex, and these 
differences have been supposed to indicate 
functional differences, the use of the larger 
ones being variously interpreted as (a) 
indication of large movement, (b) of the 
extent of the nerve fiber or (c) of the num- 
ber of muscle fibers which each controls. 
But differences in the sizes of these cells in 
the two hemispheres have been observed 
by Betz, and the larger size of those in the 
right hemisphere can not be explained in 
any of the ways that have been suggested. 
The Betz cells are reported to be absent in 
the guinea-pig, rabbit and rat, and we have 
no reason to suppose that these animals 
lack the ability to move or to coordinate 
SCIENCE 
325 
their movements. The recent studies have 
not usually been taken to suggest that the 
motor area is the seat or storehouse of 
motor memories, and in this respect there 
is a marked avoidance of a phrenological 
opportunity. Since the area is one of the 
most distinct histologically, and since it is 
one in connection with which extensive 
clinical and physiological observations have 
been made, it is of special interest that the 
histologists have been unable to explain in 
a satisfactory manner the reasons for the 
anatomical variations. Here, again, I 
would interpret the observations of Cush- 
ing and others on this area differently 
from Professor Pillsbury, who concludes 
that these results point to the non-mental 
function of this zone. We are not able to 
limit the localization of mental processes in 
this way, and, on the other hand, I do not 
believe that these observations can be inter- 
preted as indications of a mental localiza- 
tion. 
There are other facts which must be con- 
sidered in relation to the localization of 
supposed mental functions in the motor 
area. The principal one is the phenome- 
non of nerve anastomosis. If two motor 
nerves are cut and the distal part of one be 
connected with the central part of another, 
and, conversely, the central part of the first 
be jomed to the distal part of the second, 
there may be a return of function after a 
period of paralysis. We have no right to 
assume any anatomical alteration in the 
brain connections to account for this 
change, and the phenomenon has been in- 
terpreted, probably correctly, as a transfer 
of function. If this is to be interpreted 
in relation to any cerebral mental localiza- 
tion, it must surely be considered negative 
evidence. 
In regard to some of the other so-called 
sensory fields we have almost as much in- 
formation as regarding the one supposed . 
