Roy, I think you'll find that a 'curule leg' is a revivalist term used mainly in the USA during their Greco-Roman revival era, first quarter of the 19th century. As a leg only, IMO, it's a bit of a misnomer, as far as I know, we over here don't solely apply it to a leg.
Curule, was originally a Roman chair, used by the 'curule' or higher magistrates, with curved legs and no back so that it could be folded, made like a campstool with curved legs. It probably derived its name from the chariot (currus) in which a magistrate was conveyed to a place of judgment - it served early as a seat of judgment. Subsequently it became a sign of all higher offices right up to the emperor.
Here's a couple of examples showing what I believe are Roman curule chairs. ..
http://www.netcomuk.co.uk/~mckinley/temp/curule.jpg
However, in the common vernacular, the term Duncan Phyffe furniture has come to be synonymous with one of the styles which he produced. This style featured chairs with a thick top rail & stiles joined in one piece with the seat rail. The carving on the top rail was executed in specific motifs......thunderbolt, sheaf of wheat &/or a festoon of drapery. The lyre & the harp motifs were used as splats & a substitute for a baluster on tables with a center support. Curule legs often appeared on pieces also. 
