1907.| Localisation of Function in the Lemur’s Brain. 141 
on surface diagrams. Anteriorly and posteriorly it gradually merges into the 
types of cortex which are respectively found in frontal and post-central 
regions. , 
The second type of cortex (with smaller Betz cells) covers the area which 
lies between the extremities of the sulcus rectus and sulcus lateralis, and 
extends downwards as far as the superior wall of the Sylvian fissure. 
Superiorly it merges into the first type of motor cortex ; anteriorly into an 
area intermediate to this type and the type of the frontal cortex proper ; and 
posteriorly into one intermediate to this type and the temporal and _ post- 
central types. 
Further histological details of these two types are as follow :— 
First type of motor cortex. (Plate 4, fig. :1).—The cortex is about 2 mm. deep; the 
depth of the molecular layer is 0°17 mm., that of the pyramidal layer and granules about 
09 mm. ; that of the pallid zone in which the Betz cells lie about 0°2 mm. ; and that of 
the polymorph layer about 0°7 mm. The pyramidal cells are larger and have more pro- 
cesses than in other parts of the cortex (those of the post-central and temporal types 
most nearly approaching them in form). They are somewhat irregularly arranged, 
owing, perhaps, to the presence of the processes of the Betz cells. Granules are scattered 
in fair numbers at the bottom of the pyramidal layer, but they do not form a distinct 
layer. The infra-granular pyramids are the most typical feature of this area. They are, 
for the most part, well-formed giant pyramids (Betz cells), containing Nissl bodies and 
having several branched processes. They frequently measure as much as 60 p by 25 p, and 
are sometimes larger. This line of cells occupies a pallid zone in which only a few other 
cells are scattered, these being smaller Betz-like cells, faintly stained pyramidal cells, and 
a few granules. Some of the large Betz cells closely resemble the typical giant Betz cells 
of the cortex of the higher apes, but many are more pyramidal in shape. The tendency 
to arrangement in nests, which has been described in the human cortex, is not general, 
though it can sometimes be seen. The largest Betz cells are found immediately before 
and behind the small fissure (No. 1 in Plate 2, fig. 1), which lies in the middle of this area, 
and between it and the intercalary sulcus. 
Second type of motor cortex (Plate 4, fig. 2).—The pyramidal cells are smaller than in 
the first type. A line of darkly staining stellate cells is scattered above or among the 
granules, and the granules form a fairly well marked line. The cells which correspond in 
position to the Betz cells in the first type of motor cortex are not conspicuous either in 
size, shape, or number. But a somewhat scattered line of cells can be seen, measuring 
about 25 to 35p by 15, which are Betz-like in shape, having many branched pro- 
cesses staining more deeply than the other cells and possessing Nissl granules. The 
results of excitation and ablation of this area support the inference that this area is 
motor in funetion, although it differs considerably from the typical giganto-pyramidal 
motor cortex in the characteristics mentioned above. The definite layer of granules 
would suggest that this cortex is sensori-motor in function like the primary visual cortex of 
the calcarine region. This is best marked in the region from which ear movements were 
elicited. 
Brodmann* has also mapped out the distribution of the giant pyramids in the Lemur’s 
brain, and his results correspond fairly closely with ours. He points out that the little 
dimple (our sulcus 1 in Plate 2, fig. 1) is inconstant in position, and does not agree with 
* Loe. cit, 
