SPECIAL PHYSIOLOGY. 37 



vates the external straight muscle, and presides over the 

 movements outwards ; its destruction consequently involves 

 an internal strabismus. 



Trifacial (5th pair, or nervus trigeminus). This nerve 

 is composed (two roots) of centripetal (sensitive) and of 

 centrifugal fibres (motory or secretory). 



Certain fibres have been named trophic, but, as there is a 



food deal of discussion in regard to their existence, it is 

 ardly worth while to consider these in this work ; disturb- 

 ance of nutrition (trophic) observed after section of the tri- 

 facial, as well as of many other nerves, is dependent on loss 

 of sensation to external injuries (Snellen), or to vaso-motor 

 disturbances (Schiff). These fibres are distributed through 

 the three branches of the trifacial. 



The opthalmic nerve (or first division of the fifth pair) 

 presides over sensation in the skin of the forehead, of the 

 root and back of the nose, of the upper eyelid, over the sen- 

 sation in the conjunctiva, of the cornea, of the iris, and even 

 of the retina (general sensibility by means of the central 

 nerve of the retina). It furnishes secretory fibres to the lach- 

 rymal gland. 



The superior maxillary nerve presides over sensation of 

 the lower eyelid, of the cheek, of the wing or side of the nose, 

 of the upper lip, of the nasal mucous membrane (general sen- 

 sibility), of the teeth of the upper jaw, etc. It furnishes 

 secretory filaments to the glands of these different regions, 

 and particularly to the glands of the olfactory mucous mem- 

 brane. The motor branches which it appears to send off are 

 but fibres of reflexion that come from the facial by a very 

 complicated path (large superficial petrosal of the vidian 

 nerve). 



The inferior maxillary nerve presides over the sensation 

 of the teeth of the lower jaw, of the skin of the chin, of the 

 lower lip, of the auriculo-temporal region, of the buccal and 

 lingual mucous membrane ^ it moreover presides over the 

 special sensibility of the anterior half of the tongue (sense of 

 taste), and the lingual nerve (lingual branch of the fifth 

 pair) is generally .considered as the nerve of this special sense. 

 Though the chorda tym,pani may be concerned in the sense 

 of taste, yet in all cases, gustatory nervous filaments are sent 

 off by the trifacial, but by a complicated path which is not 

 yet settled by physiologists (Lussana, Schiff). This nerve 

 furnishes motory fibres to all the muscles of mastication, some 

 of which (masseter, temporal, pterygoids) elevate the jaw, 



