84 THE NERVOUS SYSTEM 



raphe. They pass horizontally forwards and blend with the 

 orbicularis oris at the angle of the mouth. When the 

 buccinator contracts, it draws the angle of the mouth back- 

 wards, but, if the angle of the mouth is fixed, e.g. by the 

 contraction of the orbicularis oris, it compresses the cheek 

 against the gum. This latter action can readily be tested if 

 the finger is placed in the groove between the gum and the 

 cheek. In paralysis of the buccinator, as also in trigeminal 

 paralysis (p. 75), portions of food tend to remain lodged in 

 this groove and, by decomposition, they impart a foul odour 

 to the breath. Further, the unopposed buccinator of the 

 sound side draws the mouth over to that side, and this de- 

 formity is very characteristic of all varieties of facial palsy. 



The Orbicularis Oris forms a sphincter muscle for the 

 mouth. It is called into action in closing the mouth and it 

 purses the lips in whistling and sucking. Other muscles, 

 which need not be detailed, aid the orbicularis in movements 

 of the lips. Paralysis of these muscles not only results in the 

 dribbling of fluids, saliva, etc., from the mouth, but also 

 renders the pronunciation of labials and labio-dentals (b, c,f, 

 m, p, o and r) slurred and indistinct. 



Before the results of intra-cranial lesions of the facial nerve 

 are described, it is necessary to refer to the path of the taste 

 fibres and the functions of the chorda tympani. 



The Chorda Tympani contains both afferent and efferent 

 fibres. The nerve begins in the descending part of the facial 

 canal and passes forwards into the tympanum. It crosses the 

 deep surface of the tympanic membrane near its upper border 

 (p. 202) and then runs through a small bony canal to gain 

 the infra-temporal fossa (pterygo-maxillary region), where it 

 joins the lingual nerve. 



It contains the taste fibres from the anterior two-thirds of 

 the tongue and the secretory fibres for the submaxillary and 

 sublingual salivary glands. The taste fibres run first in the 

 lingual and then in the chorda tympani, which conveys them 

 to the facial. In the latter they pass to the geniculate ganglion, 



