580 DISEASES OF THE ARTERIES AND LYMPHATICS. 



arteries, and where the tumour is circumscribed, a bandage, 

 in situations where it can be firmly applied, may suffice to 

 arrest the haemorrhage and produce the closure of the wound in 

 the vessel. 



I have repeatedly seen cases of diffuse aneurism from a wound 

 of the external thoracic artery, accidentally inflicted by the 

 point of the scissors whilst the horse was being " clipped," the 

 areolar tissue at the lower part of the chest being loose, and 

 admitting a large amount of blood, a huge tumour has been thus 

 formed in a short time, requiring active interference. In such 

 cases the practitioner must " cast " the animal, and operate on 

 the artery in the manner already described. 



DEGENERATIVE DISEASES OF THE ARTERIAL COATS. 



There are three forms of degeneration of the arterial coats fre- 

 quently met with in the horse. Earely, indeed, is an old subject 

 dissected at the College without some change being detected in 

 the coats of some of the large arteries. 



The most common form is " calcareous degeneration." In the 

 figure shown at page 582 this change had taken place to some 

 extent. The seat of the calcareous change is the transverse 

 fibres of the middle coat, in which it appears in the form of 

 spicula or plates, involving a greater or less extent of vessel, and 

 in some specimens it is so complete as to convert the affected 

 part into a mere passive tube. In consequence of this change 

 in the middle coat, the external surface of the artery presents an 

 uneven appearance, unequally dilated at some parts, and slightly 

 contracted at others. The internal coat may be unchanged at 

 the commencement, but it soon becomes shrivelled, irregular, and 

 ruptured at the margms of the deposit. 



In old horses this change is very common in the pos- 

 terior aorta, anterior mesenteric, the arteries of the extremi- 

 ties, the coronary (cardiac), and arteries of the brain. Indeed, 

 the so-caUed "staggers" of old horses is mostly due to this 

 degenerative change in the cerebral arteries, or death from 

 apoplexy may be due to rupture of a cerebral artery which has 

 been thus rendered friable and easily ruptured. 



Calcareous deposition differs from true bone in important 

 particulars ; it is without fibrous structure and vascularity j it 



