412 Proceedings of the Royal Society of Edinburgh. [Sess. 
A comparison of figs. 1 and 3 will show that the distribution of the 
motor cortex in fig. 3 coincides to a large extent with the distribution of 
Type II. of the histological classification ; it also overlaps into the areas 
occupied by Type I. and Type III. As the significance of this coincidence 
between the motor area as delimited by electrical stimulation, and the area 
showing large pyramidal cells in the infra-granular zone has already been 
referred to, it is unnecessary to do more than point out the similarity in 
the areas. 
6. Conclusions. 
The results of this investigation are of special interest when compared 
with the work done on the brain of insectivora by Watson (36). If the 
interesting conclusions he came to be accepted, they throw considerable 
light upon the significance of the cerebral lamination in the guinea-pig. 
In the cerebrum of the mole, shrew, and hedgehog, Watson found that 
the motor area occupied an extensive area relative to the size of the brain. 
This is also seen in the guinea-pig, as both histological examination and 
electrical stimulation locate the motor area over the greater part of the 
posterior half of the cerebrum. It is seen from the histological description 
that the lamination in the so-called motor area is not characteristic of 
exclusive motor function, as both supra-granular, or pyramidal and granular, 
layers are present. This type of cortex was described in the motor area of 
the mole by Watson ; and Bolton suggested that the area, besides regulating 
the passage of efferent impulses, was also a centre for the reception of 
sensory impulses projected to it from the various sensory areas. 
This certainly seems to be the case in the “ motor ” cortex of the guinea- 
pig, for the large pyramidal cells in the sub-granular zone are practically 
an addition to a cortex which is in other characteristics sensory. The 
probable function of the large pyramidal sub-granular cells has already 
been discussed ; they are evidently associated with movement, as they occur 
in the area over which electrical stimulation produced movement. The fact 
that they extend beyond the area figured as “ motor ” in fig. 9 is not 
unfavourable to this view, since this area really coincides with their richest 
distribution. In no part of the cerebrum is there anything like a brusque 
line between the various types of cortex; the distribution of the large 
pyramidal sub-granular cells is therefore limited by no definite line. 
Bolton’s view with regard to the sensori-motor nature of the area 
associated with movement in the lower mammals is similar to that of 
Horsley and others regarding the sensori-motor nature of the Rolandic area 
in the higher apes and in man. 
