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Dr. Cunningham—Surface Anatomy of the Primate Cerebrum. 59

Gratiolet was well aware of the great distinction which exists between
man and the apes in the relative length of the occipital lobes. He states
that in man this lobe is " extremely reduced" ; and he formulates the law
that the more highly organized a member of the group is, the smaller is the
relative size of the occipital lobes. The truth of this is at once seen by
placing the occipital indices of the cynocephalus, orang, and man, in
apposition with each other.

Occipital Indices.
Cynocephalus, 29*7. Orang, 23-2. Man, 21-2.

But quite as striking a difference between man and the ape is the
small relative size of the parietal lobe in the latter. This is very evident
to the eye in Plate viii., where we have several apes' heads depicted with
the brains exposed in situ. It would be an interesting field for speculation
to consider whether this parietal increase in the human brain has anything
to do with the acquisition of the educated movements of the limbs—more
especially of the upper limbs, and that wonderful harmony of action which
exists between the brain and the hands, and which has played so important
a part in the development of the species.

We must now study the relation which the parieto-occipital fissure at
the point where it cuts the mesial border presents to the cranial wall. In
entering upon this part of our investigation we must decide whether we
are to examine the fissure in its relation to the lambdoid suture or to the
lambda. The latter point or apex of the occipital bone lies in the mesial
plane, whilst the fissure is placed at some distance to the outer side of this,
Therefore, if we chose the lambda as our cranial point, it is necessary to
draw a straight line outward from it at right angles to the mesial plane
of the head, and note the position of the fissure with reference to this
line. Notwithstanding the inconvenience of this proceeding there cannot
be a doubt but that the lambda is the best point from which to make our
measurements. At the same time I may mention that I strongly suspect
that the discrepancies which characterize the results of many observers

[8*]