Freiburger historische Bestände - digital

172

Cunningham Memoirs.

depression. Further, I have looked in vain for a vessel occupying the
bottom of the fissure. At no period of growth can this be discovered.
A vein presenting the connexions described by Krause can generally be
seen coursing upon the anterior bounding lip of the fissure, but I have
never observed this vein tightly drawn across the surface of the hemisphere
, and never placed accurately between its lips.

We have noted that a deep annectant gyrus may be observed in the
fissure of Rolando of the chimpanzee and orang, similar to that which we
have described in man as occupying the furrow at the junction of its
upper and middle thirds. We may assume, therefore, that the interrupted
form of development of this sulcus holds good amongst the anthropoid apes
as well as in man. With regard to the lower apes, we have no evidence
one way or the other. The development of the fissures in the brain of the
apes is still virtually unknown ; and if we examine the bottom of the fissure
of Rolando and the other primary furrows in a low ape we find a uniform
depth throughout, and an absolute absence of deep annectant gyri. It is
dangerous to argue from the adult condition alone, but still the appearances
are such as would lead us to infer that the continuous and not the disrupted
form of development of the primary fissures holds good amongst the lower
apes.

In man and in the anthropoids the development of the fissure of
Rolando is in every respect on a line with that of the other two radial
" Primarfurchen" (viz. the praecentral and the intraparietal), the only
differences being that it is unprovided with a horizontal part, and that its
two vertical portions rapidly fuse with each other. In the case of the
praecentral sulcus, the two vertical parts (viz. the prsecentralis inferior and
the prsecentralis superior) as a general rule remain apart. The intervening
portion of cerebral cortex remains on the surface. The two vertical portions
of the intraparietal sulcus, on the other hand, usually run together, as in
the case of the fissure of Rolando. In 19-1 per cent., however, of cerebral
hemispheres they remain distinct; whereas the non-union of the two portions
of the Rolandic sulcus, according to Heschl, occurs in only 0'3 per cent.

But in man, as we have observed, a third lower element may be added
to the Rolandic fissure in the shape of the inferior transverse sulcus of