This disease is so called, because in some cases it pierces right through the thinnest part of the hind leg, or appears on either side immediately before the point of the hock. It, however, is often single. It is rarely present without bog spavin; and in every instance which the author has examined, it communicated with the large synovial articulation of the joint. [Illustration: THOROUGH-PIN.] It is provoked by the same causes as generate bog spavin; it is similar to that disorder in not being generally accompanied by lameness, and in being liable to the same fearful changes. Pressure and rest are the best remedies; pressure, applied after the manner recommended for wind-galls, may in some cases answer. The bog spavin and the =thorough-pin=, however, should not in every case be treated at the same time; as a general rule, it is prudent only to attack one affection by means of an India-rubber bandage. This should be so cut as to release the bog spavin from all pressure; and where the slightest uneasiness is evinced, all bandages should be instantly removed, while the corks and cloths--employed as for wind-galls--are taken off the thorough-pin. It is never well to attempt to cure the bog spavin first; the treatment ought always to commence with the thorough-pin; therefore, for a horse which will not endure the bandage, a truss must be procured from the instrument-maker. The truss is of the ordinary description, only adapted to bear upon the parts. This will probably act with efficacy equal to the bandage. When the truss has performed its office, then a perfect India-rubber bandage may be safely applied. Only, mind and also employ with the last the corks and cloths; else, when endeavoring to remove one disorder, you may reproduce another. Watch the animal while wearing the bandage; on the slightest change, either in habit or appearance, remove the India-rubber. Should the pressure affect the skin, (as it will in certain cases,) rags, thoroughly wetted, should be wrapped round the hock before lacing the bandage up. If the rags appear to be of no avail, it is better to forbear for a time, and to renew the attempt hereafter. [Illustration: DISSECTION OF THOROUGH-PIN AND BOG SPAVIN, DEMONSTRATING THE JUNCTION OF THE TWO AFFECTIONS. ]