Fig. 4

Distinctive structural features of the upper and lower eyelids in Strigiformes compared to Accipitriformes and Falconiformes. (a), (e) and (n) – Northern Hawk Owl; (b), (f) and (o) – Eurasian Eagle-Owl; (c) and (i) – Snowy Owl; (d) and (m) – Boreal Owl; (g) – Ural Owl; (h) and (o) – Tawny Owl; (l) – Little Owl; (j) – Philippine Scops-Owl; (k) – Western Barn Owl. at – adipose tissue, ap – adipose pad, bm – bundle of muscle, bv – blood vessels, cf. – collagen fibres, ef + rf – elastic fibres and reticular fibres. b, c, e, f, h, i, j, l = Mayer’s H&E stain; a, d, g, k, m – o = Movat pentachrome (modified Russel-Movat) stain. Scale bars: f, g, k = 200 μm; e, h, i = 100 μm; a – d, l, j, n, o = 50 μm; m = 20 μm