mouth, jaw
頜 centers on the lower part of the face: the mouth and jaw as physical structures.
頜 combines 合 (which may contribute a sound element) with 頁 (head), pointing to a part of the head related to the mouth or jaw. The exact historical development is uncertain.
The left side 合 looks like a container with a lid, and the right side 頁 is a head. Imagine the container opening and closing like a jaw on a head: 頜 is the mouth and jaw.
For カン, picture a can being opened by a jaw-like tool: can -> カン, and the jaw clamps down on the can.