rotula
/ˈrɒtjʊlə/ /ˈrɒtʃʊlə/noun
1 Anatomy. The patella (kneecap). Now rare.
2 Astronomy. A mechanical device showing the motion of the sun and moon and their position for each day of the year. More fully astronomical rotula. Now historical.
- The astronomical rotula was devised by the Scottish inventor James Ferguson (1710–76)..
3 Zoology. A keyhole urchin or sand dollar of the West African genus Rotula (order Clypeasteroida), having a round, flattened test with deep notches along the edge. Also (in form Rotula): the genus itself.
4Each of five radial elements forming part of the oral apparatus (Aristotle's lantern) of echinoids.
- They are elongated in shape in regular echinoids, but were named by Des Moulins (1835) from the more discoid structures that he observed in clypeasteroids (sand dollars)..
5A circular structure forming the end of some sponge spicules; = rotule. Also: a wheel-shaped spicule in the integument of certain holothurians. Now rare.
Origin
Late Middle English; earliest use found in Lanfranc's Science of Cirurgie. From classical Latin rotula small wheel, in post-classical Latin also kneecap from rota wheel + -ula. Compare Middle French, French rotule, Spanish rótula, both in sense ‘kneecap’.
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