Freiburger historische Bestände - digital

46

Cunningham Memoirs.

friiher erw'ahnten occipitalen Falten friiherer Stadien, obschon sie wie diese
Totalfalten im His'sclien Sinne sind."

Ecker* expresses himself on this question with considerable doubt and
caution. " Moreover," he remarks, "it appears to me that one of the
latter, viz. the fissura parieto-occipitalis is formed out of one of the
temporary furrows, although I do not venture to assert this." This statement
is rendered all the more ambiguous by the fact that in his description
of the brain of a third-month foetus he asserts that the occipital lobe does
not exist. Undoubtedly the fissure in dispute (the precursor of the parietooccipital
) is present at this stage. Further, he figures the parieto-occipital
and the calcarine fissures in a brain at the fourth month, although he
appears to infer that they arise more frequently in the course of the fifth
month.

According to Mihalkovics,*j* the calcarine fissure is the first to appear.
It is formed at the end of the third month, and arises with the outgrowth of
the occipital lobe almost simultaneously with the transitory furrows. The
parieto-occipital sulcus is formed shortly after it at the commencement of
the fourth month.

Having now stated the views of those authors who have dealt with this
question, I shall proceed to state the conclusions at which I have arrived
regarding the development of the parieto-occipital and calcarine fissures in
the course of my study of the complete fissures.

At the same time, that the radial transitory fissures appear on the
medial face of the hemisphere (towards the end of the second month or it
may be at the beginning of the third month) two fissures which have a
synchronous origin and lie in series with these, occupy positions which
give them a close resemblance to the parieto-occipital and calcarine fissures
of the fully developed brain. Between them is placed the primitive
cuneus. I have never seen these fissures absent; and in all good illustrations
of the medial face of the hemisphere at this stage of development (v.
Kolliker, Richter, &c.) they are represented. We have already referred to

* "Zur Entwicklungsgesch.ich.te der Eurchen und Windungen der Grosshirnhemispharen im
Eoetus des Menschen," Archiv fur Anthrop., 1869.

j- Eutwicklungsgeschichte des Grehirns. Leipzig, 1887.