TKIFACIAL NERVE. 191 



nute directions laid down by Bernard, we will quote from 

 him in brief the different steps. 



The nerve may be divided in the cranial cavity with tol- 

 erable certainty in rabbits, cats, dogs, and Guinea-pigs, but 

 it is most easily done in rabbits. It is difficult, from the 

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

 certain amount of dexterity, to be acquired only by 

 practice. The instrument used is represented in' 

 Fig. 9. It is made by Messrs. Tiemann & Co., of 

 Kew York. 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 su- 

 perior border of the condyle, directing the point of 

 the instrument slightly forward to avoid passing 

 into the substance of the petrous portion of the tem- 

 poral bone, and thus passes more easily into the 

 middle temporal fossa ; at the same time the instru- 

 ment 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 be- 

 coming free, the pressure is arrested and the instru- 

 ment 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 gradu- 

 ally, as the instrument penetrates, pressing on the bone, the 

 resistance of which can be easily recognized. Soon, how- 



113 



