No. I.] THE VERTEBRATE EAR. 137 



from the ganglion formed on the root of the N. lineae lateralis 

 or from that nerve itself. The root of the N. lineae lateralis re- 

 ceives its most anterior fibres at this age close to and a little 

 above and behind the root of the N. acousticus." 



" Piercing the membranes that separate the cranial cavity 

 from the labyrinth, it runs directly backv^ard, close to their 

 outer surface and just above the posterior branch of the N. 

 acusticus, in which there are numerous ganglion cells. It 

 passes through the upper part of the main root of the glosso- 

 pharyngeal, receiving there an important addition to its fibres, 

 and, continuing backward immediately external to the origins 

 of the anterior roots of the organs, it issues through the main 

 foramen of that nerve." 



In several instances the same nerve supplies sense organs 

 which have had a divergent differentiation, as canal and pit 

 organs. 



• The essential features of the innervation of the sense organs 

 and their relation to the canals of the head region are clearly 

 shown in Cut 25, which is reproduced from Fig. 49, PI. XLII, 

 of Allis's paper. The sense organs 16 and 17 of the infra-orbi- 

 tal system are neighbors in the now continuous canal formed 

 by the union of the facial and glossopharyngeal sections of 

 the canal system, which, as a comparison of Figs. 23-28, PL 

 XXXVII, with the views of heads given in previous plates of 

 Allis's paper and with the figure here produced, very clearly 

 show, have grown together from independent sources. These 

 figures also illustrate the interlocking of the territories supplied 

 by independent nerves unusually well, for by their aid we are 

 enabled to follow step by step the approach and final overlap- 

 ping of neighboring territories. For example, the canal systems 

 of the VII and IX nerves, although beginning their growth at 

 entirely separated centres, grow towards each other and finally 

 unite, the two systems opening out upon the surface at the 

 junction by a common pore. (See stages of this growth on 

 PI. XXXVII, and the adult condition as illustrated in Cut 25.) 

 As shown in cut, although the canals fuse to a continuous 

 channel and the sense organs are approached nearer to each 

 other, the nerves and organs are as distinctly separated as 

 though the surface structures were entirely independent. The 

 two nerves supplying this region of the common canal are 



