They are exquisite, with Dorset buttons and stunning lace. I am unable to see the lace close up, but it does look to me more likely to be the first half of the 19th century, rather than the second.
I am guessing that they were simply quite snuggly worn at the wrist, and the long sleeves came down over the top, so that to all intents and purposes it looked as though the lace was sewn to the inside of the hem of the sleeve, which of course it wasn't. They could then be popped off for a wash, perfect.
Were they worn with lace collars that matched?
The lace is much later in the 2 images below, but seeing the cuffs did remind me of a lace collar I sold on Antique Historika a couple of years ago:
These cuffs are not something that I have really come across before (although I am sure many other people have!).
As it happens, the wonderful Poppies Cottage have a pair of gorgeous cuffs for sale here :
The lovely lady that owns Poppies Cottage says that she is not sure of the date due to needing to date the lace (and she has a degree in historical dress), but they are similar to the pair above, and again close with Dorset buttons. The lace though seems to me to be a wee bit later, maybe 1870s or 1880s?
It goes without saying, of course, that with very small items like these, I am sure that old pieces of lace that had perhaps seen better days were re-purposed into cuffs and collars, and the same goes with the buttons - especially with the thriftier women of the nineteenth century.