GANGLIA AND NERVES OF SQUALUS 49 
incorporated into the main body of the ganglion, as in the vis- 
ceral ganglion of VII. There are at this stage five of the true 
gill slits open, but there is posterior to the last gill slit an epi- 
branchial ganglion. This is interpreted as a vestigial fifth 
branchial ganglion of X. 
32. FIRST TRUNCUS BRANCHIALIS X 
There are three rami arising from the distal and ventral end 
of the first ganglion branchialis vagi. The first nerve is the 
ramus pharyngeus (fig. 1, R.Ph.X,) which runs mesially and 
ventrally to the roof of the pharynx. The second ramus is the 
ramus pretrematicus (figs. 1 and 8, R.Pr.X,) which is sensory 
and comes into contact with the anterior border of the gill slit. 
Both these rami arise from the ganglion where it is still in con- 
tact with the epibranchial placode and will doubtless contain 
gustatory fibers. 
The posttrematic nerve (figs. 1 and 9, R.Po.X,) is large and 
arises from the extreme distal end of the ganglion. It pursues a 
course ventral and slightly caudal in the gill bar. The first 
two rami (fig. 1, Mo.1 and Mo.2) given off are motor, the third 
(fig. 1, S.1) sensory, and the fourth and fifth or terminal are 
again motor (fig. 1, Mo.3 and Mo.4). No posttrematic sensory 
ramus similar to that on IX could be detected. 
33. SECOND TRUNCUS BRANCHIALIS X 
The second branchial trunk is quite like the first, possessing 
a ramus pharyngeus (figs. 1, R.Ph.X2) and ramus pretrematicus 
(fig. 1, R.Pr.X.), both sensory and arising from that portion 
of the visceral ganglion fused to the epibranchial placode. The 
posttrematic nerve (figs. 1 and 10, R.Po.X,) arises from the dis- 
tal and ventral end of the ganglion and runs ventrally from this 
point. The first twig given off is motor, the second sensory, 
while the third and terminal twig is motor. All sensory twigs 
from the first and second pretrematic nerves turn laterally 
toward the ectoderm, while the motor twigs turn mesially to 
the primordium of the branchial musculature. 
