428 S. W. RANSON AND P. R. BILLINGSLEY 
By the degeneration and by the nicotine method, it can be shown that 
in the cat fibers run from the upper lumbar white rami to the sacral 
and coceygeal ganglia without passing through nerve cells. In the 
rabbit the nicotine method only has been tried; it gives the same results. 
We may then conclude that in the rabbit there are preganglionic fibers, 
stretching from the upper lumbar white rami to the sacral coccygeal 
ganglia. But since the sympathetic in the sacral and coccygeal region 
of the rabbit contains very few medullated fibers, it follows that the 
preganglionic fibers in this region must be non-medullated, and as they 
are medullated in the white rami they must become non-medullated in 
passing down the sympathetic chain. In other words, preganglionic 
fibers may become non-medullated some distance from their termination 
in the vertebral ganglia. 
But after all has been said it must be admitted that we are not 
in possession of a satisfactory explanation of the bundle of un- 
myelinated fibers which we have provisionally called the crescent 
and we do not know what the source of its fibers may be. 
As seen in figure 5, the myelinated fibers which constitute the 
larger oval field are of various sizes. The small fibers 1.5 to 3.5u 
in diameter are by far the most numerous. They have the size 
and appearance of white rami fibers with somewhat thicker 
sheaths than is usual on postganglionic fibers of the same caliber. 
The larger fibers are rather conspicuous but are not present in 
great numbers. They will be recognized as the large fibers of the 
white rami which, as we have seen, take their origin from the 
dorsal root ganglia. 
Sections stained with osmic acid through successive internodal 
segments from the sixth thoracic downward to the origin of the 
first splanchnic nerve show no great change in structure. There 
is obvious a rather considerable increase in area of the oval myelin- 
ated fascicle without any regular increase in the area of the 
crescent. The most noticeable feature is, however, the absolute 
and relative increase in the number of large myelinated fibers. A 
comparison of figures 5 and 6 will show that they are relatively 
much more numerous in the eleventh thoracic internodal segment 
than in the sixth. And the area of the cross-section at the 
eleventh is much greater than at the sixth. This increase in 
area is caused by the large number of fibers descending in the 
trunk to enter the splanchnic nerves. All of the large fibers of 
