258 PROCEEDINGS OF THE ACADEMY OF [March, 



(tadpole of about 18 mm.) I have been enabled to trace out such 

 a connecting cord. 



13. Regeneration of the tyrapano-Eustachian Anlage begins at 

 a period immediately precedina: the period when the fore-limbs 

 break out of the opercular cavity. 



14. The later metamorphosis of the tubal Anlarje is connected 

 with the modifications of the neighboring skeletal structures, par- 

 ticularly Avith the posterior rotation of the quadrate. By this 

 means the tubal cord comes into relation Avith the auditory region 

 of the skull and the various fragments are brought closer together, 

 so that they can readily unite. 



15. The acquisition of a lumen by the tubal Anlage takes place 

 gradually, beginning at the close of the metamorj)hosis. Details 

 apparently vary in difl^erent individuals. 



16. Completion of the tympano-Eustachian passage is efiected 

 by an outgrowth from the pharynx which unites with the tubal 

 A7ilage. 



17. The final position of the tympano-Eustachian tube between 

 the mandibular and hyoid bars is produced by the separation of 

 the latter from the (juadrate and its attachment to the auditory 

 capsule posterior to the tube. 



18. The annular cartilage arises at a stage immediately pre- 

 ceding the protrusion of the fore-limbs. Its Aiilage forms a dense 

 cellular strand derived from the perichondrium of the quadrate 

 and surrounding the tympanic portion of the tubnl Anlage. It 

 does not begin to form fully dififerentiated cartilage until after the 

 close of the metamorphosis. 



19. The stapes arises within the membrane closing the fenestra 

 ovalis. It has no connection with any of the visceral -arches. 



20. The columella auris is first met with in the early stages of 

 the metamorphosis, as a compact cellular strand extending forward 

 from the stapes and terminating imperceptibly in the connective 

 tissue. It continues to grow forward and acquires connection with 

 the quadrate. Continued growth brings it in contact with the 

 tympanic cavity. Choudrificatiou begins in the posterior portion 

 of the rod. 



