I’m kinda amazed at how much bone structure of the hooves and feet was already known back in 1866. The horse hoof is an extension of the third distal phalanx, which one might assume, if you look at the rest of the bones in a horse leg, but comparative anatomy was just emerging as a big field. Though Linnaeus made a lot of use of comparative anatomy in his classification of animals and plants, the formal study of it aside from for taxonomic classification didn’t start gaining much interest until the 1840s or so.
Anatomy of Vertebrates, vol. II. Birds and Mammals. Richard Owen, 1866.