20 F. L. LANDACRE 
34. Third truncus'branchitahis ext. 4-eeeeeee ee oe oe oe ee eee 50 
35. Hourthitruncusibranchia lis exer ea eee eee eee 50 
36. “The ‘ganglion visceralle Xs. at seer ac Gee Aarne sonic «nate eee See BS 50 
37; Ramis svisceralis ac ttle eee a eee ea ee ee eee 51 
Sunimary fang discussioncstnd. rose. c us See So ee nee oe ee 51 
iteratureiciteden tere. sect. Sees oe Pea EEE eee eee 55 
1. INTRODUCTION 
Up to the present time no detailed analysis of the cerebral 
nerves of the shark has been published. A voluminous litera- 
ture covering almost every other phase of the anatomy and em- 
bryology exists, but for some reason an analysis of the cerebral 
nerves of the shark such as we now have for a number of fishes 
and amphibians and reptiles does not exist. The present study 
of the embryonic ganglia and early nerves is not offered, as, in 
any sense, a substitute for such an analysis of specimens old 
enough to show complete medullation of the nerves. The author 
has attempted an analysis similar to those made on Ameiurus 
(10), Lepidosteus (712), and Rana (12), m which it was found 
that there was a particularly favorable condition of the ganglia 
in that they were well isolated, and a development of the chief 
nerves sufficient to enable one to identify them with certainty 
when their composition was known in detail in the adult. 
The present study has the disadvantage of not being preceded 
by a careful analysis of older specimens but, like the previous 
studies mentioned, has the advantage of presenting a very simple 
condition of the various ganglia and, in cases where the nerves 
are pure or contain only one component, the morphological rela- 
tions of the ganglia and nerves make their identification a simple 
matier. On the other hand, mixed nerves and very immature 
nerves present greater difficulties and in these cases where the 
various components could not be traced definitely to their dis- 
tribution they have been identified provisionally. 
The amount of attention given to the description of nerves in 
a paper devoted ostensibly to the description of ganglia would 
be unwarranted if the exact composition of the nerves were 
known. In the absence of this information the nerves had to 
be followed with the greatest care and their description is in- 
