FISTULA OF THE EAR. 3t>3 



externa. They are also seen in horses. Their treatment is purely 

 surgical, and follows general principles. Several observers have seen 

 horns on the skin of the ear in cattle. 



Paralysis of the ear in horses is usually an accompaniment of 

 central facial paralysis. Frick has seen primary paralysis of the 

 extensor muscles of the ear after the animal had been lifted by the 

 ears. Rupture of the muscles can almost always be detected under 

 such circumstances. Recovery is sometimes protracted. 



Neuralgia of the external ear accompanied by epileptiform attacks 

 has been noted in carriage horses in which the bridle straps were 

 too short, causing the head piece to press on the base of the ear. The 

 following case of Moller's belongs to the same category. 



A horse showed powerful cramp-like movements immediately a finger 

 was introduced into one or other ear. Passing it into the left ear, the 

 horse at once endeavoured to bring the left hind-foot as near the ear as 

 possible, and rapid movements were made with the muscles of the hind- 

 foot and of the neck. Pressure on the base of the ear immediately 

 produced these cramp-like movements. The same happened on the right 

 side. Pressure of the bit caused similar symptoms, so that the animal 

 was useless for work. Examination of the ears and auditory opening 

 during life showed no change ; hearing was undisturbed. Unfortunately 

 Moller was unable to make a post-mortem. 



(4.) FISTULA OF THE EAR. DENTIGEROUS CYSTS. 



Fistulae are sometimes seen in the horse at the base and near the 

 anterior surface of the conchal cartilage, extending downwards towards 

 the malar bone for a distance of 1 to 1£ inches. A little serous fluid 

 or pus discharges on pressure. On introducing a probe, at the bottom 

 of the canal a hard body may be discovered which, if the canal be 

 laid open, will be recognised as of the nature of a tooth (dentigerous 

 cyst). Sometimes several small teeth are found in the cyst. 

 Strictly speaking, the condition is not a fistula, but represents the 

 remainder of the incompletely developed branchial arch. On this 

 account the fistula sometimes communicates with the guttural pouch. 



The phenomenon must be referred to the development of embryonic 

 branchial arches and clefts. Sometimes the lateral plates of these visceral 

 cavities are ruptured, and remain so, thus giving rise to fissures in the ear, 

 pharynx, oesophagus, and neck (fistula auris et colli congenita), whilst 

 partial persistence of the unruptured embryonic furrows produces blind 

 sacs and dermoid cysts. The dental furrow which occurs in this portion 

 of the embryonic apparatus results from a primitive fold of the buccal 

 epithelium, which, as in the jaw, can produce enamel. The teeth are 

 oftenest found in the squamous portion of the malar bone. Several — i.e., 

 from 2 to 4 — may be present ; they resemble molars. Sometimes a sinus 

 alone is present, and the tooth wanting. 



