994 



THE NERVE SYSTEM 



supraorbital foramen; that of the second through the infraorbital foramen; and the third through 

 the mental foramen. The supraorbital foramen is situated at the junction of the internal and 

 middle third of the supraorbital arch. If a straight line is drawn from this point to the lower 

 border of the mandible, so that it passes between the two bicuspid teeth of the mandible, it will 

 pass over the infraorbital and mental foramina, the former being situated about one centimetre 

 (two-fifths of an inch) below the margin of the orbit, and the latter varying in position according 

 to the age of the individual. In the adult it is midway between the upper and lower borders of 

 the mandible; in the child it is nearer the lower border; and in the edentulous jaw of old age 

 it is close to the upper margin. 



Applied Anatomy. In fracture of the base of the skull the trigeminal nerve or one of its 

 branches may be injured. It seems certain that occasionally, though seldom, the trigeminal 

 nerve may be actually divided by such an injury. The trigeminal nerve may be affected in its 

 entirety, or its sensor or motor root may be affected, or one of its primary main divisions. In 

 injury to the sensor root there is anesthesia of the half of the face on the side of the lesion, with 

 the exception of the skin over the parotid gland; insensibility of the conjunctiva, followed, if 

 the eye is not temporarily protected with a watch glass, by destructive inflammation of the cornea, 



6UPRATROCHLEAR N 



SUPRAORBITAL N. 



INFRATROCHLEAR N 



NASAL NERVE 



BUCCAL NERVE 



MENTAL NERVE 



TEMPORAL BR. 

 OF TEMPORO-MALAR 



MALAR BR. OF 

 TEMPORO-MALAR 



AURICULO-TEMPORAL 

 NERVE 



Fio. 737. Sensor areas of the head, showing the general distribution of the three divisions of the fifth 

 nerve. Gerrish's Anatomy. (Modified from Testut.) 



partly, it is held, from loss of trophic influence, and partly it is certain, from .the irritation pro- 

 duced by the presence of foreign bodies on it, which are not perceived by the patient, and there- 

 fore not expelled by the act of winking; dryness of the nose, loss to a considerable extent of the 

 sense of taste, and diminished secretion of the lacrimal and salivary glands. In injury to the 

 motor root there is impaired action of the mandible from paralysis of the muscles of mastication 

 on the affected side. 



The trigeminal nerve is often the seat of neuralgia, and each of the three divisions has been 

 divided or a portion of the nerve excised for this affection. The supraorbital nerve may be ex- 

 posed by making an incision an inch and a halHn length along the supraorbital margin below the 

 eyebrow, which is to be drawn upward, the centre of the incision corresponding to the supra- 

 orbital notch. The skin and Orbicularis palpebrarum having been divided, the nerve can be 

 easily found emerging from the notch and lying in some loose cellular tissue. It should be drawn 

 up by a blunt hook and divided, or, what is better, a portion of it should be removed. 



The infraorbital nerve has been divided at its exit by an incision on the cheek; or the floor of the 

 orbit has been exposed, the infraorbital canal opened up, and the anterior part of the nerve 

 resected; or the whole nerve, together with Meckel's ganglion as far back as the foramen rotun- 

 dum, has been removed. This latter operation, though undoubtedly a severe proceeding, 

 appears to have been followed by better results than has nerve resection. The operation is per- 

 formed as tcl'ows. The maxilla is first exposed by a T-shaped incision, one limb of the incision 



