THE ORIGIN OF THE CRANIAL GANGLIA IN 

 AMEIURUS 



r 



F. L. LANDACRE 



EIGHTY-EIGHT FIGURES 



CONTENTS 



Introduction 309 



Historical sketch 312 



Material and method 322 



The differentiation of the neural plate 325 



The differentiation of the Gasserian ganglion 330 



The origin of the lateralis Vllth ganglia 332 



The auditory vesicle and auditory ganglion 334 



The fate of the preauditory placode 339 



The origin of the geniculate ganglion 342 



The differentiation of the postauditory lateral mass 349 



The origin of the lateralis Xth and the early stages of the postauditory placode 353 

 The fate of the postauditory placode and the appearance of the lateral line 



organs of the body 355 



The placodal ganglion of the IXth nerve 362 



The origin of the lateralis IXth ganglion 369 



The origin of the third and fourth epibranchial placodes . 373 



The origin of the fifth and sixth epibranchial placodes 375 



The later history of the lateral mass ganglia of the Xth 378 



General summary 384 



Bibliography 389 



Abbreviations 392 



Explanation of figures 394 



INTRODUCTION 



The origin and relationship of the cerebral nerves have been, 

 since the appearance of Balfour's classical researches on the 

 nerves of Elasmobranchs in 1876, among the most interesting 

 and puzzling problems in vertebrate morphology. Notwith- 



