§ 5 The So-Called Dual
Parts of the body which are double (ears, eyes, hands, arms, shoulders, knees, etc.), when mentioned in reference to the two ears, eyes, etc. of the same person, are expressed by a compound with the numeral deu, two, prefixed to the singular. The Welsh and Breton grammarians call this a dual. When eyes, ears, etc. are mentioned as belonging to more than one person, the plural is formed in one of the usual ways. Thus:—
lâv, hand; dual deulâv.
lagas, eye; dual deulagas; pl. lagasow.
scovorn, ear; dual deuscovorn; pl. scovornow.
glîn, knee; dual deulin.
elin, elbow; deulin.
bregh, arm; deuvregh.
bron, breast; deuvron.
scoudh, shoulder; deuscoudh.
For hands in general the plural is formed from dorn (which means more exactly fist), dornow; there is, as in Welsh, no regular plural of lâv. A variant of glîn is penglin (lit. knee-end), with a dual pedndewlin, cf. Welsh penelin, elbow.
Lastly, the plural of dên, man, is almost always tîs (earlier tus), folk, though Lhuyd gives dynion as well.