204 THE SURGICAL ANATOMY OF THE HORSE 



THROMBOSIS 



Thrombosis of arteries of the hind limb is not uncommon, the arteries 

 most frequently affected being the external iliacs. The thrombus is 

 usually the result of the arrest of an embolus which has been carried in 

 the blood stream along the posterior aorta, and in this connection it may 

 be remarked that the horse is occasionally the subject of a peculiar 

 aneurism which affects the anterior mesenteric artery. 



Emboli broken off from a thrombus in this situation thus get carried 

 to the internal or external iliac arteries, or both, and when the lumen of 

 the vessel becomes so small as to arrest its further progress, it leads to the 

 formation of a thrombus in the vessel in which it has become fixed. If 

 the emboli get into the small collateral branches before becoming arrested 

 the consequences are usually not serious, since the parts are supplied with 

 blood by the neighbouring collateral vessels. When the large vessels are 

 blocked much more serious results follow, the blood supply of the muscles 

 to which the vessel concerned is distributed, is cut off, so that these muscles 

 are not able to perform their ordinary functions. Lameness thus frequently 

 follows, the nature of which depends upon the muscles which are affected. 



When the animal is at rest there is little to be observed, but the 

 symptoms present themselves as soon as exercise is taken. Rest again 

 quickly causes them to disappear, so that the lameness is intermittent. 

 The animal may be brought out of the stable and placed in the shafts. 

 He may travel for a short distance without inconvenience of any kind and 

 then gradually collapse. After remaining down for a short time he is 

 frequently able to rise and proceed for some distance without displaying 

 signs of lameness when a second collapse occurs, and so on. 



When the thrombus is in the external iliac artery, the quadriceps 

 muscles are affected, so that the animal is unable to fix the stifle joint, and 

 symptoms are presented which are not unlike those of crural paralysis, a 

 point which will be readily appreciated. 



