or of its principal branches is of
very rare occurrence in horses.

Etiology.--Partial or complete obstruction of arteries (brachial or
others) occurs as the result of direct injury to the vessel wall from
compression and tension of muscles and resultant arteritis; lodging of
emboli; and parasitic invasion of vessel walls causing internal
arteritis.

Symptomatology.--If sufficient collateral circulation exists to supply
the parts with blood, no inconvenience is manifested while the subject
is at rest. Where the lumen of the affected vessel is not completely
occluded, there may be no manifestation of lameness when the ailing
animal is moderately exercised. Consequently, the degree of lameness
depends upon the extent of the obstruction to circulation; and,
likewise, the course and prognosis depend upon the character and extent
of such obstruction.

In severe cases, lameness is markedly increased by causing the animal to
travel at a fast pace for only a short distance. There are evinced
symptoms of pain, muscular tremors and sudation, but the affected member
remains dry and there is a marked difference of temperature between the
normal areas and the cool anemic parts. When the subject is allowed to
rest, circulation is not taxed, and there is a return to the original
and apparently normal condition, only to recur again with exertion. This
condition characterizes thrombosis.

Treatment.--In these cases, little if any good directly results from
any sort of treatment in the way of medication. Absolute rest is thought
to be helpful. Potassium iodid, alkaline agents such as ammonium
carbonate and potassium carbonate, have been administered. Circulatory
stimulants also have been given, but it is doubtful if any good has come
from medication.

Fracture of Humerus.

The shaft of the humerus, protected as it is by heavy muscles, is not
frequently fractured; and fractures of its less protected parts, as for
example, the head, are complicated in such manner that resultant
arthritis soon constitutes the more serious condition.

As a result of falls on frozen ground, kicks or any other form of heavy
contusion, the humerus is occasionally broken. It is rarely fractured
otherwise. Because of the force of contusions usually required to effect
humeral fracture, the manner in which the bone is broken, with respect
to direction, is variable. Often oblique fractures exist and
occasionally there occurs multiple fracture. In additio