THORACIC TRUNCUS SYMPATHICUS 411 
segment in three and from the second lumbar ganglion in one. 
Since it is well known that fibers of the splanchnic nerve come 
from segments as high as the fifth and sixth thoracic, it is obvious 
that these fibers must have descended in the sympathetic trunk 
to the point of origin of the splanchnic nerve. In man these 
same fibers leave the trunk in small bundles from the level of 
the fifth or sixth thoracic ganglia downward to the ninth, and 
these bundles are then gathered together to form the greater 
splanchnic nerve. In the cat other splanchnic nerves are given 
off somewhat irregularly from the upper five lumbar ganglia 
and internodal segments. 
The thoracic rami communicantes. It is not necessary to review 
the early literature dealing with the rami communicantes, since 
the work of Gaskell (86) may be regarded as the starting point 
of modern investigations on this subject. He made a careful 
histological examination of the spinal nerves and rami com- 
municantes. The gray rami were found to be composed chiefly 
of unmyelinated and the white rami chiefly of myelinated fibers. 
In the roots of the spinal nerves only myelinated fibers were 
found. He argued that, since he found only myelinated fibers in 
the roots of the spinal nerves as they left the spinal cord, the 
only connection between the spinal cord and sympathetic trunk 
must be by way of the myelinated white rami, and that through 
them occurred the only possible outflow of visceral efferent fibers 
from the spinal cord. The ventral roots of those spinal nerves 
which he found associated with white rami, the second thoracic 
to the second lumbar inclusive, were seen to contain large num- 
bers of fine myelinated fibers like those in the white rami, while 
the ventral roots of the other spinal nerves contained very few 
such fibers. These he regarded as visceral efferent fibers. <A 
gray ramus was found associated with each spinal nerve. On- 
reaching the nerve such a ramus was seen to divide, one part 
passing centrally, the other peripherally. Most of the unmyelin- 
ated fibers which ran centrally were seen to pass into the sheath 
of the nerve and become lost in the dense layers of connective 
tissue within the intervertebral foramen. Since no unmyelin- 
ated fibers could be found in the ventral roots nor in the dorsal 
