The header character is framed by a box, then variant engravings of the characters found on bronzes and other documents are listed, together with the names of the pieces it was found on.
KangXi ZiDian
These are vertical entries with some explanation of the characters (I've snipped other long extracts). Header characters are larger, pronunciation follows, then meaning and 'sightings' in known works of literature or other dictionaries.
Modern ShangWu Xin ZiDian
A Japanese Dictionary - Benesse ISBN 4-8288-0422-6
A Korean Dictionary - ISBN 89-327-0039-7
A Chinese-Vietnamese Dictionary : Han-Yue CiDian - ISBN 7-100-01454-9
The skewness of the header glyph is due to the character being near the inner margin of the page during scanning.
A Hakka dictionary : Hak-Yin Ci Tien [Ke-Ying CiDian] - MacIver 1926
Interestingly, the other dictionaries do not give the following middle graphic varient, which is found in this Hakka dialect dictionary.
Dylan W.H. Sung.