No. I.] 



THE VERTEBRATE EAR. 



145 



cept that the group of branchlets supplying the sacculus leave 

 the acoustic nerve as a trunk, almost immediately divide into 



era 



Cut i^. — The details of the nerve supply in Menopoma allegheniensis. cr.a., 

 cr.p., cr.e., the nerve branches of the anterior, posterior, and external ampullae 

 respectively, ni.ab., nerve to the crista acustica abortiva. pp-b., ramulus papillse 

 basilaris. jn.s., the nerve supply of the macula sacculi. 7}i.u., the nerve supply of the 

 macula utriculi. 



two, and then each branch breaks up into a bundle of branch- 

 lets. Among the Anura, however, there appears a new branch- 

 let from the cochlear nerve, which supplies the now discrete 

 pars basilaris, the nerve having been split off from the lagenar 

 branch in connection with the budding off of the pars basilaris. 



Among the Reptilia and Aves we notice a greater complica- 

 tion of the sense organ called pars basilaris, indeed of the whole 

 cochlea, which involves the increase in size and the modification 

 of the distribution of its nerve. 



Here we begin to observe that fateful distortion of the ear 

 chambers which has perhaps more than anything else retarded 

 our progress in the knowledge of the significance of the parts 

 of the ear and their actual relations to each other. The great 

 development of the cochlea drags the posterior half downwards, 

 backwards, and outwards in such a way as to give one the 

 impression that the ear is divided primatively into superior and 

 inferior portions. The division into anterior and posterior por- 

 tions, which I have shown above to exist in the Cyclostomes 

 and Elasmobranchs, obtains also in the Reptiles and Birds. 



Among the higher Reptilia and the Birds the cochlear nerve 

 has become the largest branch. The branchlet to the crista 



