602 HANDBOOK OF PHYSIOLOGY. 



face and head, with the exception of the skin of the parotid region 

 (which derives branches from the cervical spinal nerves), acquire com- 

 mon sensibility; and among these parts may be included the organs of 

 special sense, from which common sensations are conveyed through the 

 fifth nerve, and their special sensations through their several nerves of 

 special sense. The muscles, also, of the face and lower jaw acquire 

 muscular sensibility, through the filaments of the ganglionic portion of 

 the fifth nerve distributed to them with their proper motor nerves. The 

 sensory function of the branches of the greater division of the fifth nerve 

 is proved, by all the usual evidences, such as their distribution in parts 

 that are sensitive and not capable of muscular contraction, the exceeding 

 sensibility of some of these parts, their loss of sensation when the nerve 

 is paralyzed or divided, the pain without convulsions produced by mor- 

 bid or experimental irritation of the trunk or branches of the nerve, 

 and the analogy of this portion of the fifth to the posterior root of the 

 spinal nerve. 



Other Functions. In relation to muscular movements, the branches 

 of the greater or ganglionic portion of the fifth nerve exercise a mani- 

 fold influence on the movements of the muscles of the head and face 

 and other parts in which they are distributed. They do so, in the first 

 place (), by providing the muscles themselves with that sensibility 

 without which the mind, being unconscious of their position and state, 

 cannot voluntarily exercise them. It is, probably, for conferring this 

 sensibility on the muscles, that the branches of the fifth nerve commu- 

 nicate so frequently with those of the facial and hypoglossal, and the 

 nerves of the muscles of the eye; and it is because of the loss of this 

 sensibility that when the fifth nerve is divided, animals are always slow 

 and awkward in the movement of the muscles of the face and head, or 

 hold them still, or guide their movements by the sight of the objects 

 toward which they wish to move. 



(ft.) Again, the fifth nerve has an indirect influence on the muscular 

 movements, by conveying sensations of the state and position of the skin 

 and other parts: which the mind perceiving, is enabled to determine 

 appropriate acts. Thus, when the fifth nerve or the infra-orbital branch 

 is divided, the movement of the lips in feeding may cease, or be imper- 

 fect. 



(c.) An intimate connection with muscular movements through the 

 many reflex acts of muscles of which it is the necessary excitant. Hence, 

 when it is divided and can no longer convey impressions to the nervous 

 centres to be thence reflected, the irritation of the conjunctiva produces 

 no closure of the eye, the mechanical irritation of the nose excites no 

 sneezing. 



(d.) Through its ciliary branches and the branch which forms the 



