524 MANUAL OF PHYSIOLOGY. 



ventricle, is much the smaller of the two, and has been compared 

 to the anterior root of a spinal nerve. The large sensory division 

 springs from a very extensive tract, which can be traced from the 

 pons Varolii through the medulla to the lower limit of the olivary 

 body, and on to the posterior cornua of the spinal marrow. This 

 set of fibres has been likened to the posterior root of a spinal 

 nerve, being somewhat analogous to it in origin, function, and the 

 fact that there is a large ganglion on it within the cranium. 



The distribution and peripheral connections of this nerve are 

 somewhat complicated, and should be carefully studied when the 

 manifold functions of its branches are being considered. The 

 various impulses conveyed by the trifacial nerves may be thus 

 enumerated : 



i. EFFERENT FIBRES. 



1. Motor. To the muscles of (1) mastication, viz., temporal 

 masseters, both pterygoids, mylohyoid, and the anterior part of 

 the digastrica ; (2) to the tensor muscle of the soft palate ; and (3) 

 to the tensor tympani. (4) In some animals (rabbit) nerve fila- 

 ments also pass to the dilator muscle of the iris, reaching the eye- 

 ball by the ciliary ganglion. 



2. Secretory. The efferent impulses which stimulate the cells 

 of the lachrymal gland to increased action, pass along the branches 

 of the ophthalmic division of this nerve. 



3. Vaso-motor. The nerves governing the muscles of the blood- 

 vessels of the eye, of the lower jaw, and of the mucous membrane 

 of the cheeks and gums. 



4. Trophic. On account of the impairment of nutrition of the 

 eye and the mucous membrane of the mouth, which occurs after 

 injury of the fifth nerve, it is said to carry fibres which preside 

 over the trophic arrangements of these parts. 



ii. AFFERENT FIBRES. 



1. Sensory. All three divisions of the trifacial nerve may be 

 said to terminate in cutaneous nerves, by which the ordinary sen- 

 sory impulses are carried from (1) the entire skin of the face, 

 and the anterior surface of the external ear; (2) from the exter- 



