143 
The truncus now courses downwards and forwards, 
and almost at once divides into an upper palatine + pre- 
trematic branch and a lower R. post-trematicus (post. 2). 
The former gives off 3 RR. pharyngei (ph. wv. 2) to the roof 
of the mouth, and is then continued downwards on to the 
second branchial arch as the R. pre-trematicus (pre. 2). 
The latter, as it passes forwards, gives off from its upper 
border two motor twigs not shown in the chart, and finally 
breaks up as usual into two branches, which pass on to the 
third branchial arch, and the distribution of which is 
essentially the same as the corresponding divisions of the 
first branchial trunk. 
3.—T. branchialis tertius Vagi (¢. #. 3). 
Arises from the ventral edge of the compound 
ganglionic mass. ‘The two nerves it contributes to the 
pharyngeal plexus have been described above. Another 
nerve not shown on the chart arises posteriorly and 
internally from the base of the truncus. It passes sharply 
downwards and backwards to the roof of the pharynx. 
The truncus itself, directly it leaves the ganglion, divides 
into a palatine + pre-trematic branch coursing gradually 
downwards and forwards, and a R. post-trematicus, pass- 
ing sharply downwards and backwards. ‘The former 
divides as usual into a R. pharyngeus (ph. w. 3) anda R. 
pre-trematicus (pre. 3), the latter passing on to the third 
branchial arch. The R. post-trematicus (post. 5) breaks up 
into the usual two branches much sooner than usual, as in 
Menidia. The anterior one gives off at once in front a 
motor branch. Both pass on to the fourth branchial arch 
and are distributed as usual. 
The T. branchialis quartus vagi is so closely asso- 
ciated with the remainder of the vagus that it cannot be 
