Johnston, Nerves of Petromyzonts. 599 



For illustration of the endings of the fibers in the walls of blood 

 vessels I have taken one from thi wall of the aorta (fig, 24) and 

 one from the wall of the inferior jugular vein (fig. 25). The end- 

 ing in the aorta is seen in longitudinal section and many such 

 endings are to be found. The fibers which lead to them come 

 from the direction of the sympathetic trunk. The endings in the 

 jugular vein are seen in surface view and all the fibers in the draw- 

 ing belong to the ventral trunk of the sympathetic. There is no 

 possibility of doubt as to these endings being in the wall of the 

 vein, for the next section above passes through the empty space 

 dorsal to the vein and the next section downward passes through 

 the lumen of the vein containing blood corpuscles. From thise 

 facts it may be concluded that in the adult lamprey a large system 

 of fibers makes its exit from the brain with the VII nerve which 

 functions in connection with ths control of the circulation at least 

 in the branchial region. Whether fibers join this from other nerve 

 roots still remains questionable, and also to what extent the system 

 is developed in the post-branchial region. 



Peripheral ganglia. — Ganglion cells are found impregnated in 

 various places about the head in several series of sections. One 

 is shown in close connection with a ventral spinal nerve root in 

 the lower part of fig. 14. This is the only one I have noticed in 

 this position. A few cells are seen in connection with the sym- 

 pathetic trunks above described, but not so many are impreg- 

 nated in connection with these trunks as one would expect. Many 

 cells are found immediately beneath the parietal muscle ventral 

 to the orbit. In one series of sections more than one hundred 

 sharply impregnated cells were counted in fifteen sections through 

 the region ventral to the orbit and lateral and ventral to the sub- 

 ocular cartilage. In fig. 26 are shown some cells in this region. 

 The vertical striations bounded by a dotted line indicate the 

 parietal muscle, the oblique striations the muscle of the first gill 

 sac. The fibers lying on the gill sac are motor, except the finest, 

 which are sympathetic. At the border of the parietal muscle is 

 seen a bundle of fibers which is probably the termination ofthe 

 hypoglossus. There is one nerve cell among these fibers and 

 farther forward are three cells among fine fibers most of which are 

 of sympathetic nature. These latter cells and fibers are drawn 

 to a higher scale in fig. 27. There are some indications that the 

 fine fibers among which such cells lie follow blood vessels. In fig. 



