Ranma (欄間)

Ranma are small transom windows between rooms that are fitted above the fusuma sliding doors. Their origins are unclear, but they seem to have been around in the Heian period, with their present form having been established by the Muromachi period. 

In the beginning, their sole purpose was to let air flow and light pass, and their design was quite simple. In the Momoyama period, however, this changed and ranma began to get more and more sophisticated, with artful carvings adorning them. 

In Kyōto's machiya, the most common types of ranma are sukashi ranma with natural motives or the family crest, and osa ranma, which are not adorned in any way, but feature some simple latticework.