News Finding: "However, our dissections found between five and seven neurovascular bundles per forelimb, suggesting that additional toes begin to develop, but do not become fully differentiated."
Paper Finding: This further supports the identities of the ventral ridges and textured regions in the monodactyl and tridactyl horses as lost digits I and V. The digit identities of the fragments as I and V in Hypohippus are confirmed by carpal articulations; the rudiment of I articulates with the trapezium, and the rudiment of V articulates with the unciform.
News Context: "These findings show that today's horse is not truly monodactyl, and earlier ancestors were not in fact tridactyl or tetradactyl, that is, three-toed or four-toed." The team also discovered neurovascular evidence in support of the five-digit theory, with dissections of modern equine fetus forelimbs revealing a greater number of arteries and nerves than would be expected in a single digit. "However, our dissections found between five and seven neurovascular bundles per forelimb, suggesting that additional toes begin to develop, but do not become fully differentiated."
Paper Context: These rudiments of the incomplete metacarpals I and V are in the same position as the ventral surface irregularities in Equus, Dinohippus and Mesohippus. This further supports the identities of the ventral ridges and textured regions in the monodactyl and tridactyl horses as lost digits I and V. The digit identities of the fragments as I and V in Hypohippus are confirmed by carpal articulations; the rudiment of I articulates with the trapezium, and the rudiment of V articulates with the unciform. Interestingly, despite a reduction in the number of complete digits and an increase in their size, the overall positions of individual elements and their borders in the manus has remained consistent throughout equid evolution.