Posts made with forked trunks that divide naturally into two branches at their upper end are called in Japanese mata-ki bashira (股木柱) lit. ‘crotch-tree-post’. Sitting a ridge pole or wall beam/plate in the ‘crotch’ and lashing it to the post is among the simplest and most reliable methods of joining these two members, and requires little to no technical skill to construct, so the technique is often seen in utility structures such as storehouses and charcoal huts where more refined methods are either not required or not achievable. No doubt mata-ki were also prized by the builders of the pit-dwellings of prehistoric Japan, but no physical remains of these timber and thatch dwellings have survived.
Mata-gi bashira supporting the ridge pole on a primitive open-walled structure.
When mata-ki bashira are found in minka, their incorporation into the structure is often more sophisticated, giving the impression that the builders relished the design challenges and aesthetic possibilities these irregular timbers presented. In the doma of the Takano House in Shioyama, Yamagata Prefecture, designated an important cultural property, there is a 60cm diameter chestnut post whose upper end is left in its natural, forked state. The posts passes right through the second storey to bear the floor beams of the the upper second storey; not only the crotch of the post but also the legs support these beams, with the beam supported by the legs running perpendicular to the beam in the crotch. These upper floors, used to dry hay and medicinal herbs, storage, and sericulture, are examples of ‘zara-ban-yuka’, lit. ‘rough board floor’, i.e. thin slat-like floorboards laid with generous gaps between them to facilitate ventilation.
The massive mata-gi bashira in the Takano House
In the Hirakawa house in Maruoka, Fukuoka Prefecture, the mata-ki bashira are used at the four corners of the jou-ya and ge-ya, with each post carrying loads in two directions, from both jōya and geya wall beams. Even if the ‘legs’ of the post are cut off level at the ‘crotch’, the ‘flare’ of the timber remains, and provides a wider bearing surface to accommodate multiple horizontal members.
Mata-gi bashira in the Hirakawa House.
This method avoids the need for complicated joints at the corners, and is sturdy and structurally satisfactory, with the caveat that because a moment (torque) is induced in the eccentrically loaded post there is a tendency over time for the foot of the post to twist. This is an issue where posts are tenoned into ground sills, i.e. rotationally constrained, but was not a concern in minka which employed the horidate-bashira method of setting posts directly into the ground (a method which was still common even in the early 19th century in more isolated rural areas), as the base of the post is free to rotate in its hole.
Another mata-gi bashira in the Hirakawa House. The front ‘leg’ seems to have been cut off at the crotch and supports a large transverse beam. The rear leg remains and supports a smaller beam at a higher level. Note also the large natural concavity on the left-hand side of the post
Mata-gi-bashira are often seen in the minka of the Hokuriku region and vicinity, where they attracted some colourful local names befitting their unusual appearance. More generally they were called dōshiyō-bashira, which might be translated as ‘either way post’. In old Etchū province, modern day Toyama Prefecture, they were called ‘rabbit posts’ usagi-bashira, due to the resemblance of the forked end to a rabbit’s ears; in the northern part of old Hida Province, now northern Gifu Prefecture, they were called ‘peek posts’, by association with the act of ‘crotch peeking’ i.e. bending over at the waist and looking backwards and upside-down through one’s own legs.