82 THE NERVOUS SYSTEM 



and the stylo-hyoid. No description of the actions, etc., of 

 these muscles is necessary, as their investigation is rarely 

 called for in cases of facial paralysis. 



In the parotid gland the facial nerve passes forwards across 

 the lateral aspect of the neck of the mandible, and, in this 

 situation, it is exposed to injury, e.g. by the application of 

 forceps during delivery. As the fascial sheath of the gland 

 is so strong that even a slight enlargement of the parotid may 

 be sufficient to exert pressure on the nerve, facial paralysis 

 may be a complication of acute parotitis. 



The terminal branches of the facial nerve arise within the 

 parotid gland and they supply all the muscles of facial 

 expression, including the buccinator, the platysma and the 

 frontalis. 



PERIPHERAL LESIONS OF THE FACIAL NERVE. In complete 

 facial paralysis, due to a lesion outside the skull, all the 

 muscles of expression are completely paralysed. As a result, 

 the affected side of the face is immobile and the natural skin 

 creases disappear. 



The Orbicularis Oculi (Palpebrarum) lies partly in the eye- 

 lids and partly around the margins of the base (external 

 aperture) of the orbit. It acts as a sphincter of the eyelids 

 and its tonus serves to keep the puncta lacrimalia closely 

 applied to the surface of the eye (p. 210). When this muscle 

 is paralysed, the eye remains open and attempts to close it 

 result only in upward rotation of the eyeball. The con- 

 junctival reflex is therefore abolished, but automatic winking 

 does not cease and the eye may become closed during sleep. 

 These two latter movements are due to relaxation of the 

 levator palpebne superioris. In addition, paralysis of the 

 orbicularis oculi is accompanied by the condition of epiphora 

 (p. 210). 



The Buccinator forms the muscular stratum of the cheek. 

 Its fibres arise from the inner alveolar borders of the 

 mandible and maxilla, opposite the molar teeth, and also 

 from a ligamentous band, termed the pterygo-mandibular 



