Freiburger historische Bestände - digital

104

Cunningham Memoirs.

has not yet attained its full degree of backward extension. In all the subsequent
changes which occur in this region the sulcus centralis remains
absolutely fixed and stationary, and sways neither in a forward nor in a
backward direction.

The prsecentral sulcus is developed a little later than the central sulcus,
but as a general rule it comes into view before the end of the fifth month
(PI. ii., figs. 13, 17, 19, and 20, i). It lies accurately inline with the sulcus
praecentralis inferior on the surface of the frontal lobe; but in its subsequent
history it is not so stationary as the sulcus centralis. In the last four
weeks of foetal life its upper end generally moves forwards to a slight
extent, so that, in a measure, it loses its accurate relationship to the
corresponding sulcus on the surface of the mantle. Another peculiarity
of this sulcus consists in the fact that in the early stages of its development
it outstrips the central sulcus, and for a time it becomes the best
marked furrow on the surface of the insula. This pre-eminence it generally
loses in the eighth month. In fact, as we have seen, it is in the adult the
feeblest sulcus of the series. In connexion with this it is of interest to
note that very much the same thing frequently occurs in the case of the
prsecentral fissure of the frontal lobe. In many cases, more especially
when it appears earlier than the fissure of Rolando, it is extremely deep,
and much the most evident of the three radial " Primarfurchen" on the
mantle. Later on, however, it falls behind the others in its degree of
development. Pansch * held it as a law that there is a general correspondence
between the depth of a furrow and its period of origin : in other
words, the earlier a furrow makes its appearance in the foetal brain, the
deeper will it be in the adult brain in comparison with others of more
recent development. This law is no doubt true in the main, but there are
some exceptions, and the case in point is one of these.

Gruldberg,t in his excellent paper on the " Morphology of the Island of
Reil," has mistaken in the fcetal brain the sulcus praecentralis for the sulcus
centralis of the insula, and to account for its subsequent change in position

* " Einige Satze uber die Grrosshirnfaltungen," Centralblatt fur die Medicinischen Wissen-
schaften, No. 36, Sept. 8, 1877.

f Anatornisclier Anzeiger, October, 1887, No. 21.