THE CRANIAL NERVES. 473 



The fluid consequently escapes and runs over the lower part of the 

 face, unless the patient aids the paralyzed part by pressure with the 

 fingers. The difficulty in mastication results from paralysis of the 

 buccinator muscle, and the relaxed condition of the cheek. The food 

 consequently lodges between the gum and the cheek ; and the patient 

 is often obliged to remove it by mechanical means in order to complete 

 its mastication. 



The loss of power in the orbicularis also produces imperfect articu- 

 lation. The lips cannot be brought together with precision, and the 

 labials, such as B and P, are imperfectly pronounced. In cases of bilat- 

 eral paralysis, which have been sometimes observed, the features are no 

 longer deviated from their symmetrical position, but the difficulty of 

 articulation is much increased, extending to some of the vowels, such 

 as O and U, which require contraction of the orbicularis oris. This 

 affection is distinct from that known as " glosso-labio-laryngeal paraly- 

 sis " (page 445), in which articulation is also impaired. In the latter 

 disease, which is of central origin, the paralysis affects the muscles of 

 the tongue and larynx, as well as those of the lips ; in facial paralysis 

 it is confined to those which receive their filaments from the seventh 

 pair. Facial paralysis may therefore exist without danger to life. 



Crossed Action of the Facial Nerve. Minute examination of the 

 origin of this nerve indicates a transverse communication by decus- 

 sating fibres, between its nucleus on the floor of the fourth ventricle 

 and the opposite side of the tuber annulare. It has not yet been found 

 possible, however, to follow these fibres throughout, or to decide whether 

 they are root fibres which have simply passed through the nucleus, or 

 whether they originate from the nerve cells of the nucleus and thence 

 pass to the opposite side. 



That the facial nerve has in great part a crossed action is evident 

 from the results of pathological observation. Facial paralysis is a fre- 

 quent accompaniment of hemiplegia ; and in the great majority of 

 instances, that is, when the cerebral lesion is above the tuber annulare, 

 the hemiplegia of the body and limbs and the paralysis of the face are 

 on the same side with each other. The injury to the brain, therefore, 

 in such cases, produces both hemiplegia and facial paralysis on the 

 opposite side. But when the injury is lower down, in the tuber annu- 

 lare, it may affect at the same time the roots of the facial nerve outside 

 its nucleus, and the anterior pyramids above their decussation ; caus- 

 ing in this way a facial paralysis on the same side and hemiplegia on 

 the opposite side. It thus appears that the facial paralysis is on the 

 side of the cerebral lesion when this is below the nucleus, and on the 

 opposite side when it is above the nucleus or in the hemispheres. This 

 shows that the action of the facial nerve is largely a crossed action. 



The cross connection, however, between the nucleus and the opposite 

 side of the brain does not affect all the functions of this nerve. The 

 only decussation of its fibres known to exist is that which takes place at 

 the raphe on the floor of the fourth ventricle. If all the fibres of the 



