What articulates with the glenoid fossa?

The humerus
On the lateral angle of the scapula is a shallow pyriform, articular surface, the glenoid cavity (or glenoid fossa) of scapula

Comes from Greek: gléne, "socket"), which is directed lateralward and forward and articulates with the head of the humerus; it is broader below than above and its vertical diameter is the longest.