262 ANIMAL PHYSIOLOGY. [LESSON 79. 



1185. The respiratory, or branchial nerves, have their origin in 

 the branchial ganglions on either side; they ascend one lamella of 

 the gills, giving off numerous minute branches, and forming plexuses ; 

 the main respiratory trunk then descends the next lamella, giving off 

 its plexuses by the way ; arrived at the lower portion, it again as- 

 cends, but prior to doing this it sends off a branch to the fourth and 

 last lamella of the gills, when the main trunks ascend lovingly side 

 by side, giving off their minute plexuses by the way, till they reach 

 the summit. Here the fourth lamella gives off the (now attenuated) 

 main nerve, which receives a branch from the third lamella, and con- 

 tinues its course till the circuit be completed in the cephalic ganglion. 



1186. The pallial (pallium, a cloak or mantle) nerve, y, also 

 originates in the branchial ganglion ; we trace it throughout the 

 circumference of the mantle, accompanied by its fellow, &, till we 

 lose them both at the anterior portion of the body, in the cephalic 

 ganglion. 



1187. The post-pallia! nerves (?, I) arise from the branchial 

 ganglion on one side, and form a loop which terminates in the other ; 

 to end this surprising history it is only necessary to add that the 

 sympathetic nerves are given off by one cephalic ganglion, and end 

 in the other. 



1188. Reasoning from the facts adduced, it would appear that 

 the principle (so far as is known) firstly enunciated in a Lamelli- 

 branchiate mollusc, continues through the classes till it (probably) 

 culminates in man ; it is very far from reasonable that such an ar- 

 rangement pertains to these creatures alone. Whenever our dissec- 

 tions of the nervous system of man and the higher animals become 

 more perfect, it may result that the like connection of the great 

 nervous centres is equally complete. 



The looping of terminal nerves in man and the higher mam- 

 malia is well known, as witness the nerves in muscle, Fig. 352 ; this 

 seems to be confirmatory of the principle here shown to exist, exten- 

 sively, throughout the entire nervous system of an animal. Should 

 such an arrangement be generally true, there would be no difficulty 

 in understanding the phenomena of the reflex action of the nervous 

 system, together with other and important ^phenomena in connection 

 with peculiar nervous affections, to which poor humanity is prone. 

 The series of preparations in which the foregoing facts are recorded, 

 were dissected for the Hunterian Museum, where they still remain. 



