Dorsal tubercle
From Tardis Wiki, the free Doctor Who reference
Immediately following his regeneration, the Tenth Doctor noted a "slight weakness" in the dorsal tubercle of his right hand. (TV: Born Again) Less than 15 hours later, it was this hand which was cut off by a sword wielded by Fadros Pallujikaa, with the Doctor using his residual regenerative energy to grow a new one. (TV: The Christmas Invasion)
