No. I.] DEVELOPMENT OF THE EAR OF AMBLYSTOMA. 33 



EXPLANATION OF FIGURES, PLATES, AND ABBREVIATIONS USED. 



^r arachnoid; ^'^.^ auditory ganglion; «.« auditory involution; ^r brain; .carti- 

 laginous support of ramulus neglectus; ca anterior canal; caa crista acustica of ante- 

 rior canal; cae crista acustica of horizontal canal; cap crista acustica of posterior 

 canal- cd choroid plexus; ce horizontal canal; ch chorda; cp posterior canal; de 

 ductus endolymphaticus; dp ductus perilymphaticus; er indifferent layer of ectoderm; 

 « sensory layer of ectoderm; /r foramen rotundmn; / lagena; mn macula ac. neg- 

 lecta- ms macula ac. sacculi; mu macula ac. utriculi; nr neural ndge; otic cap- 

 sule; oc occipital; / pia; pab papilla ac. basilaris; par parietal bone; pb pars basi- 

 laris- pch parachordial cartilage; /. (in part .//) partition between Anlagen of pos- 

 terior and horizontal canals; // papilla ac. la-^en^; /« pars neglecta; ;- recessus 

 labvrinthi; rap ramulus ampulla posterioris of ramus posterior of auditory nerve; rn 

 ramulus neglectus of ramus posterior of auditory nerve ; . sacculus; 5. saccus endo- 

 lymphaticus; W dorsal fold of septum of horizontal canal; ...' ventral fold o sep- 

 tum of horizontal canal ; ./ canal connecting posterior ampulla with utriculus (smus 

 posterior utriculi of Retzius); spl lateral fold of septum of posterior canal; sq squa- 

 mosal bone; ss superior sinus of the utriculus; st stapes; .// hgament connecting 

 stapes with squamosal bone; /^ roof of buccal cavity; « utriculus; «. (5.z.) utriculo- 

 saccular partition; v auditory vesicle; F//- F/// auditory- facial nerve trunk; VII 

 facial nerve ; IX glossopharyngeal nerve. 



Figs 1-15 are camera drawings and in no sense diagrammatic, though some ot 

 the details were added free-hand. Figs. 16-20 are drawings of reconstructions. 

 Figs. 21-27 are plane projections of sensory areas in different developmental stages. 



Fig. I. Transection through the auditory region of an embryo shortly after the 

 appearance of the neural ridge. 



Fig. 2. Similar section of a somewhat older embryo in which the involution of the 



sensory area has begun. 



Fig. 3. Similar section of an older embryo. The neural ridge has largely disap- 

 peared and the auditory involution begins to assume the form of a cup. Owing to 

 the reagents or faulty manipulation the exact relations of the various parts of the 

 head have been disturbed. 



Fig 4 Transsection through the auditory vesicle in which the sac has become 

 completely closed, but is still connected with the ectoderm. The vesicle is seen to 

 be pyriform, and the dorsal apical portion -the Anlage of the recessus -has thinner 

 walls than other parts. 



Fig 5 Similar section of the ear of an embryo, 9 mm. in length. Ihe recessus 

 has become distinctly differentiated from the vesicle and is extending toward the 

 dorsal border of the brain. The ventral wall of the vesicle shows a much thickened 

 area, the Anlage of the sensory patches of the fully developed ear. 



Figs 6 and 7. Similar sections of an embryo of about 1 1 mm. The Anlagen ot 

 the horizontal canal and the lagena are shown. The distal end of the recessus is 

 beginning to expand into a saccus. Fig. 7 is a section in the anterior part of the 



vesicle. . -c- 9. 



Figs 8 and 9. Similar sections of a larva of 12 mm. at time of hatching. l'ig_ » 

 is of a section taken a little posterior to the opening of the recessus. Fig. 9 is of a 

 section at the posterior border of the vesicle. The Anlagen of the three semicircu- 

 lar canals have appeared, and the apex of the lagena is a thin membrane. In Hg. 9 



