40 F, L. LANDACRE 
primordia are at this time poorly developed and one or more 
of these twigs may be visceral sensory. No lateral line organ 
primordia are present at any point innervated by the truncus 
glossopharyngeus and all its sensory fibers seem to be visceral 
sensory. 
21. THE VAGUS GANGLIA 
The vagus ganglion is irregular in form. It extends in the 
longitudinal axis from the point of entrance of the IX caudad to 
the level of the third spinal ganglion. Its dorsal portion is thin 
from mesial to lateral but is continuous from the point of en- 
trance of the IX to a point directly over the dorsal border of the 
second true gill slit, from which point it extends caudally as a 
narrow strand of cells which is continuous with the first spinal 
ganglion. This proximal portion of the ganglion, which con- 
tains root fibers and the primordium of the somatic sensory or 
jugular X ganglion, is continued ventrally by five branchial 
ganglia. The anterior branchial ganglia are well isolated but the 
posterior ones are somewhat more fused. The proximal portion 
of each of the first three branchial ganglia is chiefly lateral line 
plus root fibers and will be designated as lateralis ganglia X,, 
X., X;. The distal portion of all five is visceral sensory and 
will be designated as visceral ganglia X,, Xs, X3, Xu, Xs. 
The lateral line rami arise from the dorsal and lateral borders 
of the proximal or lateral line portions, while from the distal or 
visceral portions arise the pretrematic, posttrematic and motor 
rami. All the branchial ganglia extend from their proximal 
ends in a ventral and caudal direction and all the visceral sen- 
sory ganglia of X are still in contact with their respective epi- 
branchial placodes and are still receiving cells from these sources 
as in the 20 mm. embryo (Reed 716). The proximal portion of 
the first’ two branchial ganglia (including the lateralis ganglion 
X, and the jugular ganglion associated with branchial X, and 
X,) and nearly all of the lateralis ganglion X. (including of 
course all roots of X) lie mesial to the primordium of the somatic 
musculature. The distal portiens of visceral X, and X, and 
X, lie lateral to the muscle primordium while the lateral line 
ganglion X; and the remainder of visceral X, and X; lie ven- 
