Freiburger historische Bestände - digital

342

Cunningham Memoirs.

noteworthy value. However, it is doubtful, whether, as a "level," it separates
two very different forms of representation from each other. It is certain
that in the anthropoid as in the lower apes there lies immediately around its
hinder end the most important cortical area in which the movement of the
conjugate deviation of the eyes is represented, but that this is limited to
about the posterior third of the sulcus. With this hinder part, therefore, of
the furrow, we are chiefly concerned in projecting the sulcus on the exterior
of the skull.

Age plays a very influential part in determining such projection. In
early life, while the Sylvian fissure is still high above the squamo-parietal
suture, this sulcus, which is so truly parallel to the Sylvian fissure, is correspondingly
high above the superior temporal ridge and stephanion ; but
as development proceeds, this, the inferior frontal sulcus, descends, until in
the large majority of adults it corresponds, with relatively slight deviations,
to the temporal ridge. The posterior end of the sulcus, which is so important
, terminates in the lower apes just below the horizontal limb of the
inferior prsecentral sulcus, but pointing in direction at the prsecentral angle,
i. e. the angle which the ramus horizontalis makes with the vertical stem.
The important conclusions to which observation of this fact has led Prof.
Cunningham, and the modes of conjunction of the sulci, he has stated on
page 287. From an examination of 63 hemispheres to determine not only
the exact point of conjunction, but also the direction of the furrow, I
found that the relation of this hinder end of the inferior frontal sulcus to
the inferior prsecentral sulcus was as follows*:—

It joined the anterior branch, of the ramus horizontalis ....
pointed at ,, ,, ....

the upper end of the vertical stem {%. e. the locus of bifurcation),
joined „ ,, „

,, the vertical stem.........

pointed at

in 38 per cent.
25
19
11
3
3

From this it follows that it can be topographically determined within
fairly close limits by the means employed for localizing the upper end of

* These observations completely confirm the view taken by Professor Cunningham, that in
Macacus the so-called sulcus rectus (w of Beevor and myself) is the inferior frontal sulcus
of man.