THE TRIGEMINUS. 531 



of the temporal bone, and pushed inward and a little forward, with its 

 cutting blade laid flatwise upon the surface of the petrous portion, until 

 it strikes the posterior clinoid process. It is then withdrawn slightly, 

 its cutting edge turned downward, and the fifth nerve divided where it 

 crosses the apex of the pyramid formed by the petrous portion of the 

 temporal bone. The instrument is again turned with its cutting blade 

 flatwise, and withdrawn from the skull in this position. When this 

 manoeuvre is successfully carried out, all the fibres of the fifth nerve are 

 divided at a single stroke, and the only part of the brain necessarily 

 wounded is the inferior portion of the temporal lobe. The hemorrhage 

 is small in amount, producing only a slight degree of cerebral compres- 

 sion, from which the animal soon recovers. 



The immediate effect of this operation is a complete loss of sensibility, 

 upon the operated side, in the integument and mucous membranes about 

 the face. The cornea or conjunctiva can be touched or pricked without 

 exciting an}*- movement of the eyelids ; while upon the opposite side 

 these parts retain their natural acuteness of sensibility. A probe may 

 be deeply introduced into the nasal passages, or the upper or lower lip 

 may be pierced throughout its substance with a steel needle, without 

 producing any indication of pain, or eliciting any sign of sensation on 

 the part of the animal. At the same time the power of motion in these 

 parts is unaffected. The eyelids may be opened or closed under the 

 influence of visual impressions, and the movements of the lips and other 

 parts continue to be performed in a nearly natural manner. In the cat, 

 the loss of sensibility and the persistence of the power of motion is 

 readily seen by irritating at different points the integument of the ex- 

 ternal ear, which in this animal has naturally an acute tactile sensibility. 

 If the point of a steel instrument be brought in contact, upon the 

 operated side, with the anterior part of the ear, which is supplied by 

 fibres from the third division of the fifth nerve, no effect is produced. 

 But if the same irritation be applied to the back part of the ear, which 

 is supplied by the great auricular nerve from the cervical plexus, a 

 vigorous twitching movement is at once excited. According to Longet, 

 the most violent injuries, such as exsection of the eyeball, evulsion of 

 the hairs about the lips, extraction of the teeth, or destruction of the 

 integument by the acutual cautery, may be performed after complete 

 division of the fifth nerve without causing any painful sensation. There 

 is entire anaesthesia of all the parts supplied by filaments of this nerve. 



The fifth pair is accordingly the exclusive source of sensibility in the 

 superficial regions of the face, and all parts of the nasal and buccal 

 cavities to which it is distributed. 



Painful Affections of the Fifth Pair. This nerve is also the seat of 

 all the neuralgic painful affections about the head and face. The most 

 common of these is headache ; which may be general, extending over 

 both sides of the forehead and vertex, or confined strictly to one side. 

 It often seems to be located in the nerves supplying the periosteum, 



