（解説文要約）
切羽が増えて、カネカタという運搬坑道が広がっていくと、通気の改善をしなければなりません。
このため、排気の坑道が運搬坑道と交差する十字路には、天井を切り上げて板張りの風橋を作ります。
坑道が増えると必然的に風橋も増えていくので、経費がかさむのが悩みの種でした。
As the number of coal facesincreased, Kanekata, the coal car drivesincreased in complexity as well.
In order to improve air circulation inside the mine, wooden wind tunnels were installed where exhaust drives and coal car drives met. The greater numbers of drives, the more these wind tunnels were necessary.
The construction for adding new drives needed more wind tunnels which troubled the owners of the collieries because of the huge expense.