The manus of the Narwhal, Monodon monoceros L.

Summary

• 1
  The flipper of the Narwhal has been investigated in foetal and adult stages, with special reference to the carpus.
• 2
  In the foetus, radiale, intermedium and ulnare, a single centrale, trapezoid, magnum and separate distal carpals 4 and 5 are present. There is no trace of a pisiform or of a trapezium. The centrale fuses with the intermedium. Distal carpals 4 and 5 unite to form an uneiform. In the adult there are three bones in the distal row.
• 3
  In the allied Delphinapterus (adult) the form of the flipper is similar, but the trapezoid is missing, as it is in Phocaena (Phocaenidae).
• 4
  In the Delphinidae, as illustrated by Globiocephala, trapezoid, magnum and uneiform are present.
• 5
  In broad-handed whales (Monodon, Delphinapterus, Phocaena) the number of phalanges decreases with age, in narrow-handed whales this number increases as the whale matures.
• 6
  The carpus of whales is of the interlocking type.
• 7
  A centrale has now been found during development in all mammals except some ungulates.
• 8
  Whales are the only mammals retaining traces of separate fourth and fifth distal carpals.