Professor Williams, in his Principles and Practice of Veterinary Medicine, refers to a case in which the dura mater or outermost covering of the brain attained a thickness varying from one inch at the base to several inches at the anterior part of the cranium, causing absorption of the frontal and ethmoid bones, and closing the frontal sinuses. The horse in which this was discovered had presented signs of brain disease," sleepiness, partial paralysis, blindness, and paralysis of the muscles of mastication for a considerable period before its death.

"It is very probable", Professor Williams remarks, "that this condition was the result of an injury, such as a blow upon the head, causing chronic inflammation."