Freiburger historische Bestände - digital

12

Cunningham Memoirs.

the actual period at which they first begin to be formed, and also regarding
the time at which they vanish. These statements will best be contrasted
if I place them in tabular form :—

Duration of Transitory Furrows.

Authority.

Period of Appearance.

Period of Obliteration.

Meckel.

Eighth to the ninth week.



Schmidt.

Middle of the third month.

End of the fourth month.

Ecker.

Third to the fourth month.

Commencement of the fifth month.

v. Kolliker.*

Third month.

Eifth month.

Mihalkovics.

Middle of the third month.

Commencement of the fourth month.

Romiti.

Tenth week.

End of the fourth month.

We may remark here that the description given by Schmidt hardly
agrees with his figures, because the transitory fissures are indicated by him
on the mesial surface of a cerebrum taken from an embryo at the eighth
week, which bears out the original observation of Meckel.

The difference of opinion which is shown in the above table results, no
doubt, very largely from variations in the duration of these fissures, but it
is likely that it is also in a great measure due to the almost insuperable
difficulty of giving to an embryo its proper age. The same embryo in the
hands of different observers would, I am satisfied, be reckoned at very
different periods of development. As I have stated, the embryos which I
have specially studied with the view of obtaining a knowledge of the
transitory fissures ranged from the beginning of the third month to about
the end of the fourth month. In all of these the transitory fissures were
visible. Clearly Mihalkovics is wrong in limiting the time of their
existence to one fortnight. It appears equally certain that they may begin
on the mesial face of the hemisphere as early as the eighth week. Meckel

* Entwicklungsgeschichte des Menschen und der hoheren Thiere, 1879.