SEA-FISHERIES LABORATORY. 287 



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 (jjost. 2). 

 The former gives off 3 RR. pharyngei (ph. x. 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 oif 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 (t. x. 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. x. 3) and a R. 

 pre-trematicus (pre. 3), the latter passing on to the third 

 branchial arch. The R. post-trematicus (post. 3) breaks up 

 into the usual two branches much sooner than usual, as in 

 Menidia. The anterior one gives oft' 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 



