An interesting Watch Chain in a style from the late 1800's. Called a "Memento Mori", after the Roman admonition "Sic Transit Gloria Mundi" [all glory is fleeting unto death] many were carried by Medical Practitioners or as a religious warning about preparing for eternity. 

This one is not as 'Macabre' as some of the others [Human Skulls, Human Skeletons, Brains, etc.].  

The 'Bar' is in the shape of a Key. Possible meaning; Key to the Kingdom of Heaven or the Doors of Eternity.

This  one showing it's size relative to an 18 size pocket watch. The Anatomically Correct Skull is that of a Hummingbird which happens to be the name of the Bar here in Macon, GA, that I'm known to frequent.