The Cranial Nerve Components of Petromyzon. 173 
The vagus trunk lies only a short distance above the sympa- 
thetic trunk, separated from it by one lamella of muscle. At 467 
is found a connection between the two consisting of two or three 
fibers, already mentioned. By 515 the vagus has lost its ganglion 
cells and continues caudally as a smaller, compact trunk. At 525 
a ventral branch begins to gradually separate, contains a few ganglion 
cells, and at 559 goes ventrad, passes through the constrietor musele 
to the mucosa and in 570 lies mesial to the cartilage. At 576 it 
divides into mesial and lateral branches. The mesial branch goes 
to the mucosa and divides into several branches which run along 
the base of the gill lamellae and on account of their small size can 
not be traced far. In 550 and adjoining sections there are five 
pairs of sense organs in the lining of the pharynx similar in every 
respect to those supplied by the IXth nerve. Although I could not 
trace the nerve quite to these organs I have no doubt that it sup- 
plies them and I shall call it the ramus visceralis. It is posttrema- 
tie in position as in the case of IX. 
The lateral branch goes outward, downward and backward in 
a very wavy course beneath the cartilage, has a somewhat compli- 
cated course past the cartilage of the gill opening and its museles, 
to which it gives branches, and having passed down behind the gill 
opening, it runs outward, downward and forward to the body musecles 
which it pierces (582). As there are no neuromasts here this branch 
to the skin must be regarded as general eutaneous. 
This is the first branchial nerve of the vagus complex and its 
mesjial and lateral rami may be called respectively, ramus visceralis 
and ramus musculo-cutaneous. 
Behind this first branchial nerve the vagus trunk continues with 
one or two ganglion cells in each seetion until 580, from which point 
the second ganglion of the trunk extends to 610. At about 585 the 
vagus trunk receives the ventral ramus of the fourth ventral spinal 
nerve. The course of this and other rami of spinal nerves which 
join the vagus will be deseribed in the section on the spinal nerves. 
This ramus forms a bundle on the dorsal side of the trunk which 
slips down over the lateral surface and at 632 contributes to a 
small branch which goes down over the inner face of the body 
musles and is soon lost. At 610 the ventral ramus of the 4th dor- 
sal spinal joins the vagus trunk; at 615 the ventral ramus of the 
5th ventral spinal; and at 623 the ventral ramus of the 5th dorsal 
spinal enters the vagus. 
