THE FACIAL NERVE. 



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b. The supramandibular branch (r. marginalia mandibularis) passes forward between the 

 lower lip and the chin and supplies the muscles of the lower lip. 



Its filaments communicate with those from the mental branch of the inferior dental. 



c. The i?ifrantandibular branch (r. colli) emerges from the lower margin of the parotid 

 gland and takes a downward course behind the angle of the jaw. Piercing the deep cervical 

 fascia, it passes forward in the neck and forms a series of loops beneath the platysma myoides 

 as far down as the hyoid bone. It supplies the platysma myoides. 



The nerve communicates with the superficial cervical branch of the cervical plexus. 



Transverse facial artery 



Branches of the facial nerve 



Superficial 

 temporal artery 



Practical Considerations. — The facial nerve may be the seat of spasm (tic 

 convulsif) or of paralysis. The lesion may be central or peripheral, the latter being 

 more common. When the spasm is confined to certain branches it usually involves 

 the muscles about the eyes. If only the orbicularis is involved it is called blepharO' 

 spasm ; if the adjacent muscles also are involved, spasmus nictitans. The facial nerve 

 is more frequently associated with spasrii than any other in the body, except the 

 spinal accessory. 



Facial paralysis is relatively common. If the central lesion — as a tumor, abscess 

 or hemorrhage— is limited to the facial centre in the cortex, a monoplegia of the facial 

 nerve will result, and the 



paralysis will usually be F^^- ^°^9- 



confined to the lower 

 branches of the nerve in 

 the face and neck, the 

 upper branches escaping 

 probably because of bi- 

 lateral innervation of the 

 upper muscles of the 

 face. A cortical isolated 

 paralysis of this type is 

 exceedingly uncommon. 

 If the lesion, as an apo- 

 plectic hemorrhage, is in 

 the internal capsule, a 

 hemiplegia on the same 

 side as the facial paral- 

 ysis will be associated 

 with it, and this also 

 usually occurs when 

 the lesion is cortical. A 

 lesion in the upper part 

 of the pons will give rise 

 to a similar condition, 

 but if it is in the middle or lower part of the pons the facial nerve will be paralyzed 

 on the side of the lesion, the hemiplegia being on the opposite side (crossed paral- 

 ysis). This is explained by the fact that the facial fibres cross to the opposite side 

 in the pons, while the motor fibres to the extremities and trunk cross in the medulla. 

 A lesion in the middle or lower part of the pons on one side, therefore, will involve 

 the facial fibres after they have crossed, and the motor fibres to the extremities before 

 they have crossed. Thus the facial nerve will be paralyzed on the side of the lesion, 

 and there will be a hemiplegia of the opposite side. 



The peripheral portion of the facial extends from its exit at the pons to its 

 terminal filaments on the face, but a lesion of the facial nucleus in the pons gives rise 

 to much the same symptoms as one of the nerve at its exit from the pons. Its intra- 

 cranial portion may be involved by tuberculous deposits, tumors, etc. In its long 

 course through the Fallopian canal it may be affected by swelling of the soft tissues, 

 by middle ear disease, or by fractures of the base of the skull in the middle fossa.^ 

 After it leaves the stylo-mastoid foramen it is in greatest danger, as from exposure to 

 atmospheric influences, and to accidental and operative wounds. It is especially apt 

 to be wounded in that portion which lies within the parotid gland. 



Parotid gland 



rotid duct 



Masseter muscle 



Dissection showing relations of facial nerve branches as 

 they cross masseter muscle. 



