Clue: Stubbs preserved large bone from horse's leg (4)
Answer: ULNA
Explanation: Definition: bone from horse's leg
An envelope ('preserved') of L ('large') in UNA ('Stubbs', actress – Mrs. Hudson in *Sherlock*). The bone is not only in horses, but the reference is intended to mislead the unwary into thinking of George Stubbs, noted for his paintings of horses.