190 EDWARD PHELPS ALLIS, JUN. 



are quite distinct as in the Urodela. In a common ray, or 

 skate, for example (Raia clavata, R. batis), tlie portio dura 

 arises from the medulla oblongata in close contiguity with 

 the trigeminal in front and with the auditory nerve behind. 

 It then turns outwards through a distinct canal, in front of 

 the membranous labyrinth, and reaching the exterior of the 

 auditory capsule divides into two branches, a very stout 

 posterior, and a small anterior division. Stannius (I.e., p. 57) 

 has observed ganglion corpuscles at the bifurcation so that it 

 answers to the ganglion geniculatum. 



" I. The posterior division passes outwards and backwards 

 behind and beneath the attachment of the spiracular carti- 

 lage, and behind the spiracle, just as, in the frog, it passes 

 behind and beneath the otic process of the su^spensorium and 

 behind the tympano-Eustachian canal. It then turns over 

 the hyomandibular cartilage, about the middle of its length, 

 just as, in the frog, the nerve passes over the columella auris, 

 and then divides into branches, the greater part of which are 

 distributed to that aggregation of cutaneous sensory tubes 

 which lies behind the angle of the jaw ; others go to the 

 muscles of the vicinity, and two slender branches run for- 

 wards in the inner side of the mandibular cartilage and 

 represent the chorda tympani, which, as in the Amphibia, 

 goes direct to its destination." 



Huxley thus considered the chorda tympani as a |DOst- 

 spiracular nerve, and he definitely identified it in the ramus 

 mandibularis internus facialis of Amphibia and fishes. The 

 homology of the chorda tympani with the ramus mandibularis 

 internus facialis of the Anura, which is said to have its 

 homologue in the ramus alveolaris facialis of the Urodela, is 

 now very generally accepted (Strong, Gaupp). This branch 

 of the facialis nerve cannot then be the homologue of the 

 similarly named nerve of fishes, unless that nerve also is the 

 homologue of the chorda. This subject thus clearly needs 

 further investigation, and first of all it is absolutely indis- 

 pensable to know the definite relations of the chorda of 

 mammals to the spiracular cleft. 



