Freiburger historische Bestände - digital

270

Cunningham Memoirs.

are furrows which are not stamped upon the surface of the frontal lobe so
firmly as the first and second frontal sulci. They are both furrows with a
short phylogenetic history. The middle frontal furrow is first met with
in the anthropoid apes; the sulcus frontalis mesialis is only seen in man,
and, apparently, it is more strongly marked in high than in low types of
brain.

IX. Development of the Frontal Sulci.—There is no part of the
cerebral surface on which the development of the sulci is so variable as the
outer aspect of the frontal lobe. This is not only noticeable in regard to
the time and relative order in which the various sulci appear, but also in
their mode of development. Consequently, it is extremely difficult to
arrive at definite conclusions upon many points of essential importance.
Gratiolet fell into the error of supposing that the early appearance of the
frontal furrows was a human peculiarity. This was a very natural mistake
to make, because it is by no means unusual to meet with foetal hemispheres
in which the frontal part is furrowed, whilst all the rest of the outer surface
is smooth.

Ecker* has evidently mistaken the horizontal part of the inferior
prsecentral furrow for the second frontal sulcus, and, consequently, he is in
considerable doubt as to what he should make of the true sulcus frontalis
secundus when it exists in a distinct form on the same hemisphere. An
inspection of his figure 2, Plate m., makes this manifest. The true inferior
frontal sulcus he marks /.* The same may be seen in his figure 3,
Plate iv., which represents the cerebral hemisphere of a ninth-month foetus.
In this the sulcus frontalis secundus is in two pieces, viz. one attached
to the vertical stem of the inferior prsecentral furrow, and the other free,
and a short distance in front of the basal part. These have escaped his
notice, whilst he has named the horizontal limb of the prsecentral furrow
the sulcus frontalis secundus. He recognizes, however, the presence, in
the foetal brain, of a sulcus frontalis medius, and figures it (vide his

* Zur Entwickkmgsgeschichte der Furchen und Windungen der Grosshirn-Hemispharen
Archiv fur Anthropologie. Dritter Band, 1869.