678 
THROMBOSIS OF POSTERIOR AORTA AND ITS BRANCHES. 
small diameter may produce no serious results, but where large vessels 
are plugged, the muscles served by them, no longer receiving the 
quantity of blood necessary for their functional activity, are incapable 
of sustaining severe exertion, lameness appears, the horse comes to a 
standstill, and finally myopathic paralysis of the affected muscles 
sets in. 
Whilst the animal is at rest circulation is maintained by collateral 
vessels, and it is only on movement that symptoms develop. The time 
of their appearance depends on the degree of obstruction in the vessels 
and the intensity of the muscular action. When the occluded vessels 
are small the animal may go several hundred yards, even at a fast pace, 
before lameness appears, and the symptoms vary in character according 
to the muscles involved, but thrombosis of large vessels is followed by 
symptoms of extensive muscular paralysis after even three to five minutes’ 
trotting. A few minutes’ rest produces an apparently perfect recovery. 
The intermittent lameness thus produced is quite distinctive. Thrombi 
extending to the aorta sometimes prove fatal, as shown by many reported 
cases. 
A remount showed oedematous swelling and inability to stand, first in 
one hind limb and, on the following day, in the other. On the second 
night it died, and on post-mortem examination the posterior aorta was 
found completely thrombosed at its point of bifurcation. The thrombus . 
contained a specimen of Strongylus Armatus. Cases of rupture of the 
posterior aorta and of thrombosis of the iliac arteries are described at 
length at p. 887 of Cadiot and Dollar’s <£ Clinical Veterinary Medicine 
and Surgery.” In Rutherford’s case the posterior aorta, right external 
and internal iliacs, and left internal iliac were all thrombosed. 
The disease generally develops insidiously, attention being first directed 
to it by the attacks of lameness, but when large vessels are blocked other 
well-marked symptoms are present, like dyspnoea, perspiration, and 
cramp in the affected groups of muscles. The thrombosed vessel never 
again becomes clear, though collateral circulation is sometimes established, 
and gradual improvement follows. In other cases the lameness increases, 
in consequence of the growth of the thrombus. 
Symptoms— The intermittent lameness, which soon disappears with 
rest, but always returns on movement, is characteristic. Its severity and 
extent depend on the position and size of the thrombus or thrombosed 
vessel. Blocking of the femoral artery is immediately followed by loss 
of function in the ilio-psoas and tensor fasciae latae, which it supplies 
with blood. Lameness is, therefore, most marked whilst the limb is 
being advanced. The forward stride is retarded and shortened, and the 
limb dragged, the reason being that these actions are normally performed 
by the muscles named. 
