俱舍論疏 1.250

1.250

「論曰至界成十八」，釋也。此為建立十八界故，成第六依，故六識外更立意界。已上數也。

Regarding the commentary statement from "The text says" up to "the dhātus become eighteen": this is the explanation. In order to establish the eighteen dhātus and to establish the support for the sixth, the mind dhātu is established in addition to the six consciousnesses. The above deals with the number.