TRIFACIAL, OR TRIGEMINAL NERVE. 



639 



immediate loss of sensibility upon the corresponding side of the face. Magendie was the 

 first to succeed in keeping the animals alive, observing certain interesting remote effects 

 following division of the nerve. 



The operative procedure employed by Magendie has been followed, with great suc- 

 cess, by other physiologists, particularly Bernard, to whose researches we are indebted 

 for many additional facts of interest concerning the functions of the fifth nerve. As 

 this is an operation which we have frequently performed with success, following the 

 minute directions laid down by Bernard, we shall quote from him in brief the different 

 steps : 



The nerve may be divided in the cranial cavity with tolerable certainty in rabbits, 

 cats, dogs, and Guinea-pigs, but it is most easily done in rabbits. The operation is diffi- 

 cult from the fact that one is working in the dark, and it requires a 

 certain amount of dexterity, to be acquired only by practice. The 

 instrument used is represented in Fig. 216. The operative procedure 

 is as follows : 



1. " The head of the rabbit is firmly held in the left hand. The 

 operator feels with the finger of the right hand the tubercle situated in 

 front of the ear, formed by the condyle of the lower jaw. Behind this 

 tubercle, is a hard, osseous portion, the origin of the auditory canal. 



2. "The operator penetrates just behind the superior border of the 

 condyle, directing the point of the instrument slightly forward to avoid 

 passing into the substance of the petrous portion of the temporal bone, 

 and thus passes more easily into the middle temporal fossa ; at the same 

 time the instrument is directed a little upward to avoid slipping into the 

 zygomatic fossa and thus failing to enter the cranial cavity. 



3. "As soon as the instrument has penetrated 'the cranium, which 

 is recognized by the point becoming free, the pressure is arrested and 

 the instrument is directed downward and backward, its back sliding 

 along the anterior face of the bone, which should serve as a guide in the 

 operation. 



4. "This point of departure that is to say, the anterior face of the 

 bone being found, the instrument is pushed along, following its inferior 

 border and proceeding gradually, as the instrument penetrates, pressing 

 on the bone, the resistance of which can be easily recognized. Soon, 

 however, the operator feels, at a certain depth, that the bony resistance 

 ceases : he is then on the fifth pair, and the cries of the animal give 

 evidence that the nerve is pressed upon. 



5. " It is at this moment that it is necessary to hold firmly the instru- 

 ment and the head of the animal ; then the cutting edge is turned so as 

 to be directed downward and backward, at the same time pressing in 



this direction so as to divide the nerve on the extremity of the petrous portion, behind 

 the ganglion of Gasser, if possible, or at least on the ganglion itself. 



6. " The instrument is then drawn back, pressing upon the bone so as to accomplish 

 completely the section of the trunk of the fifth pair ; then it is withdrawn by passing 

 over the same course on the anterior face of the petrous portion so as not to lacerate the 

 cerebral substance. 



" The accident to be feared in the operation is section of the carotid when the instru- 

 ment has penetrated too far, or lesion of the cavernous sinus when it is pressed too far 

 forward." 



When this operation has been performed without accident, its immediate effects are 

 very striking. The cornea and the integument and mucous membrane upon that side of 

 the head are instantaneously deprived of sensibility and may be pricked, lacerated, or 

 burned, without the slightest evidence of pain on the part of the animal. Almost always 



FIG. 216. Instru- 

 ment for di- 

 viding the fifth 

 nerve. (Bernard.) 



