Itagamama - Itagamama

…Initially, they were made from a single thick board as a structural member to bear the load from above on the bridge, but in the late Heian period, thin outlines appeared as decorative materials to be placed between kumimono (architectural kumimono) and kumimono, and they developed greatly thereafter. The former is called ita-gamagata, and the latter hon-gamagata or kuri-nuki-gamagata. In the early days of hon-gamagata, the left and right legs were made from separate diagonal members, and they retained some structural function, but from around the Kamakura period, a single board was hollowed out and carvings such as arabesque patterns were placed between the legs. …

*Some of the terminology explanations that refer to "ita-ga-kata" are listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…はじめは，虹梁上で上方の荷重を受ける構造材として1枚の厚い板から造られていたが，平安時代後期に装飾材として組物（くみもの）(建築組物)と組物の中間におく厚みの薄い輪郭だけのものが現れ，以後これが大いに発達する。前者を板蟇股，後者を本（ほん）蟇股または刳抜（くりぬき）蟇股という。本蟇股は初期には左右の脚を別々の斜材で造っており，いくらか構造材としての機能を残していたが，鎌倉期ころから1枚の板をくりぬき，両脚間に唐草などの彫刻を入れるようになる。…

※「板蟇股」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報