MUSTELUS LiEVIS. 189 



trigeminal. In the tadpole^ however, and in all the TJrodela, 

 the portio dura forms a ganglion which lies close to the 

 Gasserian, but perfectly distinct from it, and which answers 

 to the ganglion geniculatum. 



" In all the TJrodela a commissural trunk connects the 

 portio dura with the Grasserian ganglion ; this I apprehend 

 represents the nervus petrosus superficialis minor, 



" From the ganglion of the seventh, whether it be closely 

 united with that of the fifth or not, two nerves proceed — a 

 posterior and an anterior. 



"1. The posterior nerve is the larger. It passes outwards 

 in front of the auditory capsule in the frog, or beneath its 

 anterior end in the Salamander (but being in each case 

 morphologically anterior to the labyrinth), and then turns 

 outwards. In the frog it enters the tympanic cavity, and 

 keeping close beneath the tegmen tympani and in immediate 

 apposition with the outer wall of the auditory capsule, it 

 passes above the level of the fenestra ovalis and stapes, over 

 the columella auris ; and finally turning downwards appears 

 in the region between the hinder edge of the suspensorium 

 and the hyoidean arch. The course of this part of the nerve 

 is therefore precisely similar to that of the trunk of the 

 posterior or facial division of the seventh nerve in man, Avhile 

 it is contained in the Fallopian canal. Moreover, it gives off 

 an anastomotic branch to the glossopharyngeal, and supplies 

 the depressor of the mandible and hyoidean muscles. And it 

 gives off a slender branch which passes directly downwards 

 and forwards to the inner side of the articulation of the 

 mandible with the suspensorium, and runs along it to the 

 symphysis, anastomosing with the parallel mandibular branch 

 of the third division of the trigeminal. It is clear that the 

 nerve is the homologue of the chorda tympani. In all 

 respects there is a complete correspondence between the 

 posterior division of the seventh nerve in the frog and the 

 facial nerve in man 



" In osseous fishes the portio dura is very generally closely 

 united with the trigeminal, but in the Plagiostomes the nerves 



