The Cranial Nerve Components of Petromyzon 181 
Spinal ventral 4 arises in 530—535, divides in 523 into dorsal 
and ventral rami. The dorsal ramus of each of the ventral spinal 
nerves has the same course. It goes upward over the lateral sur- 
face of the lateral line nerve and on the inner surface of the dorso- 
lateral muscles into which it sends fibers, and is sooner or later 
lost. The ventral ramus goes ventro-caudad through an area of 
loose eonnective tissue between the musceles and notochord until it 
reaches the cardinal vein, when it is bent laterad aud celosely 
crowded between the vein and the museles. Here it is imbedded 
in fibrous tissue whieh stretehes obliquely ventro-laterad from the 
side of the notochord over the ceardinal vein. Some strands of this 
separate the nerve from the vein. Here the nerve is extremely 
flattened and its fibers are obliged to continue ventrad either in very 
small bundles or singly and it is extremely diffieult to trace them 
with certainty. After passing the cardinal vein the fibers collect 
into a bundle again and reach the dorsal surface of the vagus trunk. 
In some cases the nerve fuses indistinguishably with the vagus 
trunk, in some cases it can be distinguished on the lateral surface, 
and as has already been noted some of its fibers may pass on ventrad 
without joining the vagus. The ventral ramus of the 4‘% ventral 
spinal joins the vagus at about 585. 
Spinal dorsal 4 arises at about 548 and has its ganglion and 
dorsal ramus in nearly the same plane. Its ventral ramus follows 
a course similar to that which has been described for the ventral 
motor ramus, but even more intricate. As it descends toward the 
cardinal vein it runs in some cases on the inner and in some cases 
on the outer surface of a vertebral vein and when this joins the 
cardinal the nerve continues upon the lateral surface of this vein. 
Here it lies wholly mesial to the fibrous tissue and usually appears 
to pierce the wall of the cardinal vein so as to form a part of the 
boundary of the cavity of the vein. From here on it is greatly 
attenuated and runs close down over the cardinal into the angle 
between that and the vagus trunk, so that it reaches the latter at 
its dorso-mesial angle.. The ventral ramus of the 4! dorsal fuses 
with the vagus at 610. 
Spinal ventral 5 arises in sections adjacent to 580, divides into 
dorsal and ventral rami at 565, and its ventral ramus joins the 
vagus trunk at 615. 
Spinal dorsal 5 arises at 598, has its ganglion and dorsal ramus 
at 590, and its ventral ramus joins the vagus at 623. 
Morpholog. Jahrbuch. 3. 13 
