CoGHiLL, Cranial Nerves of Ainblystonia. 269 



nents. A comparison between these nerves should await thor- 

 ough embryological studies of the nervous system of the lowest 

 Mammalia. Any position taken at present upon the point must 

 be only tentative. It seems certain, however, that the chorda 

 tympani should be considered as passing morphologically in 

 front of the Eustachean tube and tympanum (Hekrick, '99, 

 p. 316) and that it should therefore be considered as a pre- 

 spiracular nerve. This being true, its most complete morpho- 

 logical and physiological representative in the Ichthj^opsida is 

 probably found in the r. alveolaris of Urodela. 



There are certain variations in the course of the r. alveo- 

 laris in Urodela which are of doubtful significance. In Ambly- 

 stoma, Salamandra (Druner, p. 493) and Triton (Druner, ' 

 p. 562) the iierve enters a canal between Meckel's cartilage 

 and the bones of the mandible. Fischer ('64) finds such a 

 canal in Siren, but Wilder ('91) denies its existence. In Pro- 

 teus and Menobranchus (Druner, pp. 592, 608) the nerve 

 passes cephalad dorsally of the musculature and mesially of the 

 mandible. Bowers, also, reports such a condition in Spelerpes. 

 The presence, also, of the anastomosis with the trigeminus in 

 the lower jaw is doubtful for some Urodela. It does not seem 

 to occur in Proteus and Menobranchus, according to Druner's 

 descriptions and is lacking in Spelerpes (Bowers). 



Druner's position with regard to the r. jugularis is best 

 stated in his own words (p. 449) : "Der R. jugularis der Uro- 

 delen tragt keine Kennzeichnen, dass in seinem Facialsantheil 

 der R. posttrematicus VII zu suchen ist. An der Stelle am 

 Knorpel des Hyoidbogens, wo man einen solchen vermuthen 

 konnte, fehlt ein Nerv — ebenso wie eine Kiemenbogenarterie 

 daneben. Sensible oder sensorische Nerven des Facialis fiir 

 den ventralen Theil der Schleimhaut der Mundhohle verlaufen 

 zwischen I. Schlundspaltentasche und I. Kiemenspalte nicht. " 



Judging, however, by the function, central origin and rela- 

 tion to the gill clefts, it is obvious that the r. jugularis and r. 

 hyoideus of the Anura are morphologically equivalent struc- 

 tures. The fact, also, that they both receive the communicat- 

 ing-nerve from the vagus is additional proof that they have a 



