Passing on to the knee, we first survey the front and feel for any enlargement of the surface, or for a nodule beneath the skin not uncommon in hunters from an embedded thorn; the hair should be raised in order to expose any scar, the result of a former broken knee. Scars here do not render a horse unsound, unless the cause which produced them has also affected the joints or structures about it in such manner as to interfere with the animal's action and usefulness.