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Figure 1 | Frontiers in Zoology

Figure 1

From: New developmental evidence supports a homeotic frameshift of digit identity in the evolution of the bird wing

Figure 1

The embryological position of the wing digits is 2, 3, 4. Collagen type 9 whole mount immunofluorescence showing relative positions of embryonic skeletal elements in a non-controversial limb, and in the bird wing. (a, b) In a pentadactyl limb, like that of the mouse (Mus musculus), the cartilage of digit 4 is spatially aligned with the ulnare and the ulna, conforming the primary axis (red line). (c, d) In the embryonic wing of the chicken (Gallus gallus), the cartilage of the posterior digit occupies the same position (red line), suggesting it is a digit 4, as in 2, 3, 4. Scale bars: a, c—500 μm.

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