1 1 4 INNEBVATION. [CHAP. XX. 



both the power of mastication was destroyed on the same side, and 

 the sensibility of the lower part of the face and tongue was lost. 

 If the nerve were divided in the cranium, the whole side of the face 

 and forehead, with the eyeball and nose, became insensible, and the 

 muscles of mastication were paralysed. Irritants might then be 

 applied to the eyeball, without exciting winking, or causing pain, 

 and strong stimulants might be introduced into the nostrils without 

 creating the least irritation. When the trunk of the nerve within 

 the cranium of an ass was irritated, the jaws closed with a snap 

 from the excitation of the motor fibres, which are distributed to 

 the muscles of mastication. 



The conclusions which we draw from anatomy and from experi- 

 ment are confirmed by the histories of cases in which the fifth nerve 

 had been diseased. In such instances we may observe the most 

 marked separation of the motor and sensitive power, when the larger 

 portion only or the two superior divisions of the nerve are affected, 

 and we find both motion and sensation destroyed when the whole 

 trunk of the nerve is involved in the disease. It is not uncommon 

 in such cases to find the eyeball totally insensible to every kind 

 of stimulus, the nose quite unexcitable by the fumes of ammonia, 

 or the most pungent vapours, and the mucous membrane of the 

 mouth so insensible to the contact of foreign matters that a morsel 

 of food will sometimes remain between the gum and the cheek 

 until it has become decomposed. The insensibility of the eyeball 

 exposes it to the permanent contact of irritating particles of dust, 

 etc., which excite destructive inflammation of its textures. The 

 whiskers may be pulled forcibly without sensation. The muscles 

 of mastication become wasted and inert, as shown by the distinct 

 depression in the regions of the masseter and temporal muscles, but 

 the superficial muscles, on which the play of the features depends, 

 preserve their natural condition. 



The fifth nerve may, therefore, be regarded as the motor nerve 

 in mastication, and the sensitive nerve to that great surface, both 

 internal and external, which belongs to the face and anterior part of 

 the cranium. ,. From its great size, and the large portion of the me- 

 dulla oblongata with which it is connected, it may excite other 

 nerves which are implanted in that centre near to it. Thus it may 

 be an excitor to the portio dura, as in winking or to the respira- 

 tory nerves, as in dashing cold water in the face, or in sneezing. 

 Its lingual portion distributed to the mucous membrane of the 

 tongue is at once a nerve of taste, touch, and common sensibility, 

 and its connexion with the papillary structure of the red parts 



