738 THE NERVOUS SYSTEM. 



Surgical Anatomy. The fifth nerve maybe affected in its entirety, or its sensory or motor 

 root may be affected, or one of its primary main divisions. In injury to the sensory root there 

 is anaesthesia 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 by destructive inflammation 

 of the cornea, partly from loss of trophic influence, and partly from the irritation produced by 

 the presence of foreign bodies on it, which are not perceived by the patient, and therefore 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 lachrymal and salivary glands. In injury to the motor 

 root there is impaired action of the lower jaw from paralysis of the muscles of mastication on 

 the affected side. 



The fifth 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 supra-orbital nerve may be 

 exposed by making an incision an inch and a half in length along the supra-orbital 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 removed. The infra-orbital 

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

 exposed, the infra-orbital 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 rotundum, has been 

 removed. This latter operation, though undoubtedly a severe proceeding, appears to have been 

 followed by the best results. The operation is performed as follows : The superior maxillary 

 bone is first exposed by a T-shaped incision, one limb passing along the lower margin of the orbit, 

 the other from the centre of this vertically down the cheek to the angle of the mouth. The 

 nerve is then found, divided, and a piece of silk tied to it as a guide. A small trephine (one- 

 half inch) is then applied to the bone below, but including, the infra-orbital foramen, and the 

 antrum opened. The trephine is now applied to the posterior wall of the antrum, and the 

 spheno-maxillary fossa exposed. The infra-orbital canal is now opened up from below by fine 

 cutting-pliers or a chisel, and the nerve drawn down into the trephine hole, it being held on the 

 stretch by means of the piece of silk ; it is severed with fine curved scissors as near the foramen 

 rotundum as possible, any branches coming off from the ganglion being also divided. 1 The 

 mental branch of the inferior dental nerve has been divided at its exit from the foramen by an 

 incision made through the mucous membrane where it is reflected from the alveolar process <m 

 to the lower lip ; or a portion of the trunk of the inferior dental nerve has been resected by an 

 incision on the cheek through the Masseter muscle, exposing the outer surface of the ramus of 

 the jaw. A trephine was then applied over the position of the inferior dental foramen and the 

 outer table removed, so as to expose the inferior dental canal. The nerve was dissected out of 

 the portion of the canal exposed, and, having been divided after its exit from the mental foramen, 

 it was by traction on the end exposed in the trephine hole, drawn out entire, and cut off as high 

 up as possible. 2 The inferior dental nerve has also been divided by an incision within the mouth, 

 the bony point guarding the inferior dental foramen forming the guide to the nerve. The buc- 

 cal nerve may be divided by an incision through the mucous membrane of the mouth and 

 the Buccinator just in front of the anterior border of the ramus of the lower jaw (Stimson). 



The lingual (gustatory) nerve is occasionally divided with thejiew of relieving _the pain in 

 cancerous disease of the tongue. This may be done in that part of its course where it lies below 

 and behind the last molar tooth. If a line is drawn from the middle of the crown of the last 

 molar tooth to the angle of the jaw, it will cross the nerve, which lies about half an inch behind 

 the tooth, parallel to the bulging alveolar ridge on the inner side of the body of the bone. If 

 the knife is entered three-quarters of an inch behind and below the last molar tooth and carried 

 down to the bone, the nerve will be divided. Hilton divided it opposite the second molar tooth, 

 where it is covered only by the mucous membrane, and Lucas pulls the tongue forward and over 

 to the opposite side, when the nerve can be seen standing out as a firm cord under the mucous 

 membrane by the side of the tongue and can be easily seized with a sharp hook and divided or 

 a portion excised. This is a simple enough operation on the cadaver, but when the disease is 

 extensive and has extended to the floor of the mouth, as is generally the case when division of 

 the nerve is required, the operation is not practicable. 



The Sixth Nerve (Fig. 393). 



The Sixth or Abducent Nerve supplies the External rectus muscle. 



Its superficial origin is by several filaments from the constricted part of the 

 pyramid, close to the pons, or from the lower border of the pons itself, in the 

 groove between this body and the medulla. Its deep origin is from the upper part 

 of the floor of the fourth ventricle, close to the median line, beneath the emirientia 

 teres. 



From the nucleus of the sixth nerve fibres pass through the posterior longi- 



1 Camochan, Amer. Journ. Med. Science, 185H, p. 136. 



2 Mears, Trans. Amer. Siirg. Assoc., vol. ii. p. 4(39. 



