Feather These barbules have minute hooks called barbicels for cross-attachment. Down feathers are fluffy because they lack barbicels, so the barbules float free of each other, allowing the down to trap air and provide excellent thermal insulation. At the base of the feather, the rachis expands to form the hollow tubular "calamus" (or quill) which inserts into a follicle in the skin. The basal part of the calamus is without vanes. This part is embedded within the skin follicle and has an opening at the base (proximal umbilicus) and a small opening on the side (distal umbilicus). Hatchling birds of some
A Donkey, 3 Rocks, and a Bird. facing one another. The donkey has a rock balanced on its back, while the bird is both standing on a rock and balancing one on its head. The donkey has surfaces decorations, including glyphs and figures, and is coated in polychrome bronze. The bird is coated in blue, green, orange, red and yellow. The sculpture measures approximately x x . Its base is made of exposed aggregate concrete and measures approximately x x . One plaque on the base reads, . Another reads, . Inscriptions near the donkey's crotch displays the artist's last name, a copyright symbol, and the year