DISEASES OF THE BRAIN AND NERVES 199 



earies of the petrous temporal bone. Concussion of the brain 

 and heinorrhcio:e of the internal ear is also a causative fac- 

 tor. Certain disease conditions of the cerebellum and medulla 

 oblongata may cause an interruption in the comhictivity of 

 the vestibular nerve. In pigeons it is o])served in contagious 

 meningitis. 



The symptoms of bilateral disease of the cochlear nerve are 

 easily recognized owing to the fact that there is complete deaf- 

 ness. If it is unilateral the symptoms may be so meager that 

 its presence entirely escapes the observation of the owner. 



Unilateral paralysis of the vestibular nerve is evidenced 

 in all species by the head being held in an oblique manner, 

 the diseased side being held lower. The head may be held 

 in a position under the 

 front part of the body with 

 the lower part of the head 

 turned back towards the 

 sound side. This turning 

 of the head may be slight 

 or 45° to 75°, but in birds 

 it may be as much as 180°. 

 or even more. If the head 

 be carried under the body 

 the dorsum of the cranium 

 may touch the ground. 

 There is frequently a hori- 

 zontal rolling of the eye- 

 balls towards the sound 

 side. There mav be diffi- 

 culty in taking food, and 

 in birds it is commonly 

 quite impossible. If the 

 disease is bilateral it closely 

 resembles cerebellar ataxia^ 

 only the symptoms are limited to the head and neck. 



If the paralysis is due to an injury, the disease as a rule 

 is not permanent and the symptoms all disappear in a few 

 days or weeks. If the condition is due to pathological changes 

 in the auditory nerve or nerves the symptoms are persistent, 

 depending on the nature of the prinuiry cause. The bird 

 may, after a while, die. 



In traumatic causes the bird needs to be kept in a quiet 

 place free from annoyances, and, if necessary, artificial feed- 

 ing is resorted to. If there has been an injury and hemor- 

 rhage takes place in the tissues, surgical interference may 

 be indicated. In cases in pigeons due to contagious menin- 



FiG. 71. Paralysis of the Auditory Nerve 

 OF A Silver Campine Hex. 



