No. I.] 



THE VERTEBRATE EAR. 



143 



carry away from the parent posterior canal organ sufficient 

 energy to enable it to multiply. 



The auditory nerve may be traced, according to Villy, in the 

 larval Rana teinporaria, long before the medulla is closed, from 

 the neural ridge to the flat plate of thickened epithelial cells 

 that later on is formed into the auditory vesicle. 



In Tadpoles 1 1 mm. in length the auditory vesicle is com- 

 pleted, and the VIII nerve passing from the brain ends in 

 contact with nearly the whole inner face of the vesicle, in the 

 form of a ganglionic swelling. During this time " the auditory 

 nerve is absolutely continuous with the facial nerve." 



cr.a. 



Cut 14. — The branches of the auditory nerve and their distribution in Amphiuma 

 means, after Retzius. cr.a., the nerve supply of the anterior ampullar organ, cr.p., the 

 nerve supply of the posterior ampullar organ, cr.e., the nerve supply of the external 

 ampullar organs. I, 2, 3, the three trunks of the auditory nerve external to the brain. 

 m.ab., the nerve supply of the abortive ampullar sense organ. r.l., the ramulus 

 lagensg of the posterior branch. m-.s., the nerve supply of the macula sacculi. 

 viAi., the nerve supply of the macula utriculi. r.a., the anterior branch of the 

 auditory nerve. 



Strong (1890, 274) has stated (p. 600): "The facial of the 

 Amphibia is divisible into two parts, very different from each 

 other : A ventral part which persists in the higher vertebrates 

 and corresponds, in part at least, to the facial of Mammalia ; 

 and a dorsal part representing in Chorophilus and Tadpoles the 

 diminished remnant of a nerve, or group of nerves, which are 

 much more important in the Urodela and remaining Ichthy- 

 opsida." 



The dorsal branch of the VII, as defined by Strong, is given 

 off immediately above the auditory ; it soon divides into two 

 branches, both of which are sensory. This branch of the VII 

 is largest in Urodela and disappears entirely in the adult Rana 



