Unidentified engraving Skull 17 th century?
 

I thought that this picture is interesting and relevant to the topic
I would like to know the engraver of the author and date, though!

Dear Paul, I think, you have an engraved frontispiece page from this book:

Autor: Helbig, Johann Lorenz. Nürnberg, Im Verlegung Johann Georg Lochners, Buchhändlers, 1730. (24), 364, (12 index) pp.; (8), 306, (4 index) pp; 2 parts in 1 volume; contemporary vellum over boards; folio 33x21cm; Nice decorated initials, head-and tailpieces; interesting engraved full-page frontispiece preceding the first part and entitled 'horologium hominis christiani'. It lists 12 pious texts according to the hours of the day and refers to a 13th hour called the "certissima haec et novissima Hora", illustrated by a human skull, bones and a snake;

For more information you should open this site: http://www.ilab.org and type "horologium hominis christiani" into the search field. Hopefully, this helps.