:\1U8TELUS L^VIS. 187 



logically a prebrancliial one. Herrick (32, p. 160), following 

 me, concludes that tlie cliorda is a prespiracular nerve because 

 of its course " through the tympanic cavity and above and in 

 front of the Eustachian tube." Dixon, however, one of the 

 latest workers on the subject, certainly shows the nerve in a 

 post- Eustachian position in a five weeks' old human embryo 

 (15, Fig. 15). The relation of the nerve to the Eustachian 

 tube in this figure cannot be mistaken, for the tube lies 

 between the facialis and the trigeminus nerves, and the chorda 

 arises from the facialis considerably beyond the tube and has 

 not a recurrent course. In an embryo seven weeks old 

 Dixon shows the nerve in Avhat would seem to be a pre- 

 Eustachian position (Fig. 9). Whether this diiference in the 

 two figures is due to some error on Dixon's part, to some error 

 in my interpretation of his figures, or to an actual change of 

 position between these ages, I am unable to judge. That 

 Dixon himself considers the nerve as a prespiracular one, in 

 the adult man, is definitely stated in one of his later works 

 (16, p. 479) ; and that the chorda changes its relations to the 

 cleft seems indicated in Broman's statement (9, p. 568) that 

 in his human embryo No. Ill, " Die hintere Spitze der ersten 

 inneren Visceralfurche, die sicli im vorigen Stadium gleich 

 hiiiter der Chorda tympani, lateral von dieser bis an die 

 Korperwand hinausstreckte, befindet sicli jetzt eben an der 

 medialen Seite der Chorda." This apparent change in the 

 relations of the two structures might be caused simply by a 

 change in the direction of the first visceral cleft, though this 

 seems improbable. In Broman's Fig. 8, PI. A, I should 

 certainly say that the chorda had a recurrent prebranchial 

 course. In his Fig. 2, PI. C, the first visceral cleft seems to 

 lie between the recurrent chorda and the trunk of the facialis, 

 the chorda thus here being postbranchial in position. These 

 apparent changes in the relation of the nerve to the cleft may, 

 possibly, be in some way related to the difference in relation 

 of the chorda to the " Ohrcolumella " in Amphibia and 

 Eeptilia, noted by Gaupp. According to that author (22, 

 p. 159) the nervus hyomandibularis facialis of Amphibia runs 



