232 Mr. Shaw on the Facial Nerves. 



Having been engaged with Mr. Bell in making the experi- 

 ments by which these facts were proved, my attention was 

 naturally called to a further observation of the condition of the 

 muscles of the face in the different kinds of paralysis. The 

 cases which I have examined during this inquiry, have induced 

 me to hope, that by following up the observations which led to 

 the discovery of the difference between the functions of the two 

 systems of nerves, we shall eventually be able to ascertain, the 

 cause of the variety of symptoms in paralysis. 



In one man, I could see no symptom of palsy until he laughed 

 or sneezed ; while in another, the features distorted by paralysis 

 regained their proper balance when the actions of laughing or 

 sneezing were excited. In a third> the paralysis was apparent, 

 not only while the features were at rest, as in the case of com- 

 mon palsy, but the distortion of the countenance, instead of 

 being diminished, was increased to a most unusual degree, 

 when the patient laughed or sneezed. 



Before attempting to account for the variety of the symptoms 

 in these cases, I propose to give a description of the nerves of 

 the face, and of the changes produced on the expression in 

 different animals, by cutting a branch of either set of nerves. 



Two nerves which arise from distinct parts of the brain, and 

 which differ from each other in structure and function, are dis- 

 tributed on the face in man, and on the corresponding parts in 

 the greater number of mammalia. 



The one hitherto called Portio Dura of the Vllth. belongs to 

 the system o{ Additional, OT Superadded Nerves, a.nd passes to 

 every muscle that is in any way connected with respiration or ex- 

 pression ; while the other, called the Vth, or Trigeminus, is one 

 of the original, or symmetrical system, and goes not only to the 

 same muscles, but also to the skin, and to the deeper muscles, 

 whose action is principally that of mastication. 



The proportion of the Facial Respiratory Nerve to the Vth. 

 is greater in man, than in any other animal. If we descend to 

 the next link in the chain of beings (the monkey,) we shall find 

 the proportion of it to be much diminished, and that of the 

 Vth increased. The distribution of the nerve is more compli- 



