DISEASES OF THE BRAIN. 303 



the current of the circulation. The embolism may also be 

 due to detachment of fragments of pulmonary thrombi. 



Cerebral thrombosis is almost always associated with an 

 unhealthy condition of the inner coat of the vessels, or to a 

 diseased condition of the blood itself. 



Embolism and thrombosis cut off the supply of blood 

 from the part of the brain to which the diseased vessel is 

 distributed, and cerebral softening ensues. 



CEREBRAL HAEMORRHAGE, OR APOPLEXY. 



Cerebral haemorrhage is due to rupture of a vessel in 

 the brain. Rupture of cerebral arteries is generally due to 

 disease of the walls or to changes in the surrounding parts 

 by which the vessels are deprived of support, or finally to 

 injury. Cerebral haemorrhage is very rarely met with in the 

 horse. 



Symptoms. — In some instances there may be premonitory 

 symptoms, but generally the horse suddenly loses conscious- 

 ness and falls prostrate to the ground. 



The extravasation, if occurring on one side of the brain, 

 gives rise to partial or complete hemiplegia, or a certain set 

 of muscles, or one limb only (monoplegia) may be para- 

 lysed, in accordance with the extent of destruction of the 

 cerebral substance. The symptoms vary in accordance with 

 the part of the brain affected, and in rare instances, owing 

 to increasing haemorrhage, may take some days before they 

 are fully developed. 



The breathing is stertorous and the pupils are usually 

 dilated and insensitive to light, and the animal is insensible 

 to external surroundings. 



The pulse is rapid and thready ; the limbs are flaccid, 

 and the body is bedewed with a cold sweat. 



When the lesion is very extensive, the coma is profound 

 and the sphincters relaxed. 



