Spinal Ganglia in Human Embryo, especially, in its Earlier Stage

Abstract

The development of peripheral nerve system in the earlier stage of embrynic life is much in advance to the other organs as well as the central nerve system. The nerve cells in the cerebrospinal ganglia are larger than any nerve cells in the central nerve system, the ganglia are grown to a enormous dimension, the processes from the cells are represented by strongly silver staining thick fibres, as are the motor fibres emerging from the ventral horns of the spinal cord, and these fibres are clearly traceable to the farthest periphery. The development of the peripheral vegetative nerve system is also very remarkable, the fibres being of the minute type and the termination being formed into the distinct terminalreticulum (Stöhr) in the 3rd and 4th month embryos already.
The sensory nerve cells in the spinal ganglia are classifiable into the two types of major and minor, the former being found at the distal, and the latter at the proximal, poles of the ganglia in general. From the number of the processes sent out by the unit cells, the three types of unipolar, bipolar and pseudo-apolar can be distinguished. But though in an incomparably smaller number, some multipolar and fenestrated cells can also be observed. The nerve processes from these cells always run out in a simple course.
Almost all the cells in the spinal ganglia of 1st month embryo belong to the pseudo-apolar cells. In later growth, these cells decrease in number, while numerous unipolar cells, a smaller number of bipolar cells and a very limited number of multipolar cells make appearance. This observation is widely at variance with the hitherto accepted genetic theory about these nerve cells.
The mantle-cell plasmodium and the connective tissue capasule surrounging the nerve cells are very poorly developed in 1st month embryo, but in 3rd and 4th month embryos, mantle-cells are observed in an increased number around the nerve cells, especially at the incipient part of the nerve processes, simultaneously with the conspicuous appearance of the incipient part, and also the development of the connective tissue capsules shows some progress. The development of these cell elements around the nerve cells reaches a nearly final stage in 2nd year infant. Thus it is presumed that the increase of the mantle-cell nuclei keeps abreast with the complication of the nerve processes running through the mantlecell plasmodium.
The pseudo-apolar cells represent the most infantile cell type in the spinal ganglia. They are provided with strongly developed processes, but the nerve fibrils at their incipient parts as well as around the cell nuclei are yet in an immature state and are not silver staining, so that these cells appear as if they lack any poles. In the later stages in the embryonic life, the immature fibrils gradually come to maturity and their silver affinity grows with it, when the pseudo-apolar cells assume the shape of polar cells.
Polar cells are very clearly observed in 3rd and 4th month embryos. Minute neuro-fibrils with silver affinity make appearance in the cell bodies and the incipient parts of the nerve processes. The unipolar cells have one process each continuous from the incipient part, which runs through the plasmodium in a very simple winding course, and the process branches out in T- or Y-shape at a considerable distance from the mother cell. However, as the running course of the incipient part grows more complicated with the growth of the body, and the process is attracted to the mother cell, the branching point apparently comes also nearer to the mother cell in adult.
The incipient part of the processes, as in other cells, often show fibril dissolution. Upon emergence from the plasmodium, the processes become nearly constant in size, showing frequent triangular fibril dissolution at the branching points.