Hemon (1995:§49)
De Arbres
49. Nouns referring to the double organs of the body generally have a dual, or special plural formed with the aid of daou- for masculines, and of di- or div- for feminines: lagad 'eye', an daoulagad 'the (two) eyes; skouarn 'ear', an diskouarn, an divskouarn 'the (two) ears'. Note I: These words in turn may be pluralized: daoulagadoù 'pairs of eyes'. Note II: Words such as lagad, skouarn, etc., when they do not designate the organs of the body, have all ordinary plural: lagadoù 'eyes', (a, spot, of grease on the surface of a liquid)' skouarnoù 'handles (of vases)'. Note III: Note the irregular forms: glin 'knee', an daoulin 'the (two)knees' dorn 'hand', an daouarn 'the (two) hands' gar 'leg', an divhar 'the (two)legs'.
reference
- Hemon, R. 1975a 1995. Breton Grammar. Translated, adapted, and revised by Michael Everson. Dublin: Everson Gunn Teoranta.