Johnston, Nerves of Petromyzonts. 595 



on the ends of small branches. This is illustrated in fig. 21 taken 

 from the ventro-lateral wall of the third gill sac. 



THE SYMPATHETIC SYSTEM. 



The sympathetic trunk. — This has been mentioned above as a 

 bundle of fibers going directly caudad from the trunk of the VII 

 nerve just beneath the auditory capsub. In position this corre- 

 sponds closely with the sympathetic trunk in P. dorsatus. As 

 the nerve runs caudad it maintains a position a little farther 

 laterad than in P. dorsatus, never approaching so close to the 

 aorta as in that species. Further, the trunk in adult Lampetra 

 is very much larger than in the ammoccetes of P. dorsatus. In 

 addition to this trunk the facialis at its ventral end sends caudad 

 another nerve which extends through at least three branchial 

 segments. This whole system of fibers seems to be related chiefly 

 or exclusively to arteries, veins and blood and lymph sinuses, and 

 it is for this reason that it is spoken of as a sympathetic sj'Stem. 

 Morphologically the dorsal trunk corresponds to the sympathetic 

 trunk in higher forms and in at least one place ganglion cells are 

 impregnated in it, which confirms the description given for P. 

 dorsatus. The ventral prolongation of the VII nerve caudad, 

 on the other hand, has no parallel known to the writer. 



The general course of these nerves is shown in figs. 2 to 11. In 

 fig. 22 is shown the sympathetic trunk as it lies over the first gill 

 sac, from a section between those drawn in figs. 3 and 4. The 

 trunk has just left the VII nerve and is runningover the muscle 

 in the anterior wall of the first gill sac. The dotted lines indicate 

 the outline of the sinus at the base of the gill. The full line to the 

 right indicates the border of the muscle whose other border is the 

 sinus. At first sight the fibers given off were taken to be motor 

 fibers, but it was found that the fibers and endings difi^er from 

 any that are known to be in muscle, that the fibers pierce the 

 muscle to the wall of the sinus beneath, and that in other sections 

 the endings of similar fibers in the walls of blood vessels is per- 

 fectly char. In this figure the fibers which run down toward the 

 left run in a fold or constriction of this sinus and are lost without 

 coming near any other organ whatever. After careful study in 

 all parts of the sections it may be stated with confidence that these 

 fibers are in no way related to muscles. Wherever the muscle 



