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Re: Two new papers on digit morphogenesis



> Frietson Galis, J.J. van Alphen, J.A. Metz, 2002.
> Digit reduction: via repatterning or developmental
> arrest? Evolution & Development 4(4):249-251

This interesting paper contains a few interesting old stipple drawings...
        One (Fig. 2A), from 1890, shows an embryonic hand of the frog
*Pelobates fuscus* with 6 fingers (including the praepollex). As Feduccia
says all the time, IV lies in a straight line with the ulna.
        Another (Fig. 2B), from 1921, shows 7 toes in an embryonic leg of
the urodele *Ambystoma tigrinum* which looks _exactly_ like the now
classical scenario: The femur splits distally into tibia and fibula, the
tibia continues in a straight line with the tibiale and the praehallux
(while the praepollex in *P. fuscus* lies at a right angle to the radius +
radiale), the fibula splits into intermedium (which continues into
unidentified centralia) and fibulare, from which a digit labeled as VI
diverges at a right angle. Then the axis continues, still in the same
straight line, through the distal tarsals of V through IV. The toes VI, V
and IV lie lateral to the axis, only then does the axis bend medially
(becoming the famous digital arch), unlike what happens in the frog hand and
in Feduccia's constant assertions.
        A third (Fig. 3, 1942) shows an embryonic hand of the lemur
*Microcebus*. A praepollex is clearly present. As in the frog, finger IV is
the straight continuation of the ulna. A postminimus, equivalent to what's
called toe VI above, is also shown and labeled (Pm), but was apparently not
as clear to see as the praepollex. It could diverge right at the ulnare
which is hard to see. Optimists could maybe recognize the pisiform (Pi) as
an 8th finger, or as a thickened distal carpal VI.

It's a reply to

Mark W. Hamrick: Developmental mechanisms of digit reduction, same issue,
247f.