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Dr. Cunningham—Surface Anatomy of the Primate Cerebrum. 31

be adduced from the fact that variations in the capacity of the hinder part
of the cranium are much greater than those in the fore part.*

Considering, then, that the occipital lobe in primates owes its origin to
a general growth of the cerebral hemisphere, and not to the sprouting out
of a local bud from its hinder end, it would be wrong to deny the presence
of a corresponding portion of the cerebrum in the lower mammals. From
this point of view, Benediktf has some ground for his assertion that in the
mammalia generally there is an occipital lobe. Upon his further statement
that the calcarine fissure is also developed in brains below the primates, I
am not in a position at present to offer an opinion.

With the expansion of the cranial cavity the temporary fissures become
obliterated by the partial opening out of the infoldings. The cerebrum at
the same time increases in length, and the occipital lobe comes clearly into
view. But the increase in length is not so great as that which would be
produced by the complete opening out of all the transitory infoldings of
the cerebral wall. This can readily be proved by measuring the depth of
the fissures and calculating the increase in length which the cerebrum has
undergone between the time when these fissures were present and the
period when it is entirely smooth. The question, therefore, arises—
What becomes of the deeper parts of the folds ? To this, I suspect, we
cannot offer a satisfactory answer. We have seen that Meckel, the original
observer of these transitory fissures, was of opinion that their obliteration
was due to the growing together of their opposed surfaces. Certain it is
that the deepest part of the bottom of the infolding cannot reach the
surface of the brain in every case unless it does so by a partial absorption
of the walls of the fold. This, combined with the partial opening out of
the fissures, may serve to account for their disappearance. Further
research, however, is required in connexion with this part of the inquiry,
and this can only be conducted by one who has a large amount of particularly
well-preserved material at his disposal.

Richter has advanced the theory that the choroid plexuses, as they

* Virchow's Gesammelte Abhandkmgen zur wissenschaftlichen Medicin, 1856.
t Der Hinterbauptslappen der Saugethiere, von Dr. Moritz Benedikt (Wien). Sep. Abdr.
a. d. Centralbl. f. d. Aled. Wissensch., 1S77, No. 10.