I 



MESENCEPHALIC ROOT 177 



directly median to the mandible. The margins of the cut skin 

 were clamped on either side to a sterile towel and the skin w^as 

 separated from the fascia below. With the aid of a probe the 

 muscles and blood-vessels of the mandibular region were sepa- 

 rated until the digastric muscle was reached, which was severed 

 through its tendinous portion and its posterior belly removed. 

 This brings the tympanic bulla (fig. 4, T.) into view. In the 

 first experiments the cephalic portion of the ventral wall of the 

 bulla was removed with the aid of a small pair of bone forceps, 

 exposing the inner ear. This incision was continued cephalad 

 and dorsad to include the removal of enough of the caudal rim of 

 the semilunar ganglion foramen to expose the roots of the trigem- 

 inal nerve. In these experiments where a portion of the ventral 

 wall of the bulla was removed I usually obtained an infection within 

 the middle ear, which developed into a good case of meningitis, 

 killing the animal about the tenth day. This was prevented in 

 the later experiments by placing a cigarette drain in the inner 

 ear before sewing up the incision, and removing it a little each 

 day after the third day. In the first experiments the trigeminal 

 roots were severed by cutting them with a small curved scalpel, 

 but since these roots were so intimately related to the circulus 

 arteriosus (Willis) inwardly and to a venous sinus outwardly, it 

 was extremely difficult to avoid injuring them. Better results 

 were afterward obtained by using an electric cautery, the needle 

 of which was bent at right angles. The best results were obtained 

 in the last experiments by keeping out of the inner ear entirely 

 and reaching the trigeminal roots with the curved electric needle 

 through the semilunar ganglion foramen. This procedure re- 

 quired an exact knowledge of the course of the trigeminal roots, 

 but no infection resulted in the middle ear, thereby eliminating 

 the trouble of draining this cavity. A double closure was made 

 of the incision, by first sewing together the fascia and lastly the 

 skin. A dressing of iodine was finally applied to the wound. 



The results of this experiment can be told by pricking the 

 maxillary and mandible regions with a needle as soon as the 

 animal has recovered from the effects of the anesthetic. If no 

 response, the experiment has been successful. In this operation 



