When paralysis is confined to muscles supplied by a particular nerve it is said to be " peripheral". The most common example of this form of the malady is that in which the seventh nerve is involved. The seventh nerve after leaving the brain emerges from the cranium through a canal in the petrous temporal bone, and on reaching the surface passes underneath the joint formed by the lower jaw and the temporal bone, and then over the cheek, where it gives off branches to the muscles of mastication, the nostrils, and the lips.
Fig. 180. - Facial Paralysis, a, Partial. B, Total.
Injury to this nerve gives rise to paralysis of the muscles of the face, hence it is termed " facial paralysis". It may occur on one side, as is mostly the case, or both nerves may be simultaneously affected.
Facial paralysis may result from injury to the nerve as it passes through the canal in the temporal bone. This may be the result of disease of that bone, or of some effusion into the sheath of the nerve from inflammatory conditions.
Injury to the nerve after leaving the canal is the more common cause, such as blows beneath the ear when rolling, or being cast, or from other causes. Pressure from tumours or abscesses, or inflammatory swelling in its course, will also produce it.
Where a nerve is paralysed the angle of the mouth on the sound side is drawn upward, while that on the paralysed side is lowered. The lips hang loose and pendulous, the eye cannot be closed, the nostril of the affected side cannot be dilated, the cheek is flaccid and has lost its firmness to the touch. In feeding, the patient seizes his food with the teeth instead of gathering it up with his lips. In drinking, the mouth is pushed into the water for some distance, and during mastication food falls from the mouth on the paralysed side.
When due to abscess or inflammatory swelling hot fomentations and poultices should be applied to the affected part.
If possible the abscess should be laid open and emptied, so as to remove the pressure on the nerve. This should be followed by iron tonics and nux vomica to restore the lost power to the muscles, and, if necessary, the application and repetition of iodine blisters. Where a tumour or inflammatory swelling exists, a purgative followed by iodide of potassium in full doses should be given.