200 CLINICAL APPLIED ANATOMY. 



ascending frontal convolution, and in the adjacent part of the 

 third frontal convolution, just below the face centre. The cortical 

 centres for the arm lie in the ascending frontal convolution above 

 the face centre. (Fig. 14, p. 183.) Consequently lesions of the 

 face centre usually involve also the centres for speech and for arm 

 movements. In a similar manner disease of the conducting tracts 

 below the face centre tends to implicate the adjacent fibres for the 

 tongue and limbs. Thus it comes about that the supranuclear 

 facial paralysis usually presents itself as part of a hemiplegia. 



The paralysis caused by a supranuclear lesion is incomplete. 

 In this type of paralysis, which is sometimes called " cerebral," 

 the weakness of the lower facial muscles is more obtrusive than 

 that of the orbicularis palpebrarum and frontal portion of the 

 occipito-frontalis muscles. The escape of the upper part of the 

 face is probably explained by the fact that the facial nucleus 

 receives fibres from both hemispheres of the brain, and some of 

 these fibres preside over the movements which are retained. 

 There is no reaction of degeneration in the paralysed muscles. 

 Emotional expression in the face and the winking reflex are 

 retained in cortical and subcortical lesions. The optic thalamus 

 appears to be concerned in emotional expression, and the winking 

 reflex depends on the integrity of the afferent fibres of the optic 

 or ophthalmic nerves, the facial nucleus and the efferent infra- 

 nuclear facial tract. The supranuclear facial tract crosses the 

 mid line about half way down the pons to reach the facial 

 nucleus. (Fig. 13, p. 182.) Lesions involving the tract above 

 the decussation cause incomplete facial paralysis on the side 

 opposite to the lesion. 



Nuclear and infranuclear lesions. Lesions below the decussa- 

 tion in the pons affect the face on the same side as that on which 

 they occur, and since they are near the nucleus of the nerve 

 usually cause complete paralysis. 



The facial nucleus lies in the ventral part of the tegmentum, 

 near the junction of the pons with the medulla. (Fig. 17, p. 191.) 

 Isolated lesions are rare. There is reason to suspect that the 

 fibres which the facial nerve distributes to the orbicularis oris 



