THE CIECULATOET SYSTEM. 221 



artery. In ' Yeterinarian/ vol. xii, p. 125, is recorded 

 a case of false aneurism outside the elbow, whicli appeared 

 suddenly. 



Thrombus. — Partial or complete plugging of a blood- 

 vessel with fibrin somewhat resembles aneurism in its 

 effects, for in each case successive layers of clot 

 line the wall of the vessel, the outer being the oldest 

 and having undergone most extensive organisation. The 

 cause of this clotting of the blood in the vessels of living 

 animals is generally some degenerative change of the 

 inner coat of the artery rendering it rough. The patho- 

 logical condition resembles that which we noticed in 

 endocarditis. The tendeucy of plugging of an artery is 

 to cut off more or less the supply of blood to the part 

 to which the branches are distributed. Generally anas- 

 tomoses of vessels atones indirectly and gradually for this. 

 Plugging of a vein is still less important. Sometimes a 

 portion of fibrin broken off from the thrombus is carried 

 in the round of the circulation and becomes forced into a 

 vessel through which it cannot pass. It becomes fixed, 

 therefore, and proves more or less detrimental according 

 to the part affected. It is termed an emholism. The 

 capillaries of the lungs, spleen, and kidneys are small and 

 so sometimes become involved in this manner. Emboli 

 and thrombi are formed in some blood diseases, especially 

 in the lungs in pleuro-pneumonia epizootica. 



Wounds op Aeteeies present no special features in the 

 ox. They are comparatively unimportant since the arteries 

 are small and are denoted by a jerky flow of bright blood. 

 Transverse cuts when the vessel is not completely severed 

 and oblique wounds are the most persistent in bleeding. 

 Such are best treated by completing the incision. The 

 ligaturing of arteries is an important part of all surgical 

 operations with the knife (see Figs 35 and 36). 



Ieeegulaeities op Aeteeies occur in the ox as in all 

 other animals, and are due to imperfection of develop- 

 ment, or to recurrence to previous type, or to higher 

 specialisation. They are seldom so important as to 

 interfere with surgical operations. 



