This sankyoku must have been the name used in contrast with ￥'heikyoku' (the music of "heike biwa" (the Japanese lute for playing the Tale of Heike)), in which the musicians of Todo-za (the traditional guild for the blind) originally engaged as a profession.
これはおそらく当道座の音楽家たちの本来の専門音楽である「平曲」（平家琵琶の音楽）に対しての名称である。