Histological Study of Auditory and Static Ganglia in Earlier Stage of Human Embryo

Abstract

I have succeeded in supplementing the currently accepted observation that only simple bipolar cells are found in the auditory and the static ganglia with a few new findings in my recent ontogenetical study on the subject.The nerve cells in the auditory and the static ganglia in earlier stage of human embryo, especially in the latter, are mostly bipolar, but there are also some multipolar, fenestrated and unipolar cells in them, the most primitive formation of all the types being represented by pseudo-apolar cells.The pseudo-apolar cells, which represent in a first month embryo the prototype of all the other above mentioned cells, decrease rapidly as the embryo grows to third and fifth months, the majority being transformed into bipolar cells. In a pseudo-apolar cell, the development of the protoplasm surrounding the cell nucleus and the incipient parts of the processes emerging from it being very low as yet, the nerve fibrils therein are too immature to be silver-affine, so that the cell itself shows the appearance of apolarity in a preparation. Later on, with the maturation of the above mentioned parts, these cells take the form of polar cells.When an embryo reaches the age of three months, the nerve cells begin to show the distinction of major and minor types. The larger cells predominate far over the smaller ones in number, and the development of nerve fibrils is more rapid and powerful in the former. In a fifth month embryo the above outlined observations become more apparent, almost no pseudo-apolar cells being found persisting. The nerve cells in the auditory ganglia are smaller than those in the static ganglia, the proportion of size being approximately 2 to 3.Of the bipolar cells occupying the numerical majority in the cells of the auditory and the static ganglia, the two nerve processes generally start from opposite poles of the cell body, but in many cases, the points of emergence are very closely situated. One of the two processes runs peripherally and the other centrally. The size of the two processes is different in most cases, but no regularity is observable in their relative thickness. It is very interesting that some bipolar cells are found, of which both the processes bifurcate in Y shape, soon after emergence.A small quantity of unipolar cells are found contained in the static ganglia. These are somewhat different from those observed by MIKAMI (1953) in the spinal ganglia of early embryos, in that the single process emerging from a pole of such a cell bifurcates in T or Y shape at a short distance from the cell and the two branches run peripherally and centrally respectively.A considerable number of multipolar cells, similar to those found by MIKAMI (1953) in the spinal ganglia of embryos in the earlier stage, is found in the static ganglia. These multipolar cells tend to appear in groups, belong to the major type of nerve cells and send out from three to six processes per cell. The processes emerge from irregularly spaced points on the cell surface, and in general two of the processes are long, each running peripherally and centrally; the other short processes extend circumferentially and end freely after or without branching. Beside the above usual type, multipolar cells are not rarely found that are somewhat differently formed. For example, in some quadripolar cells, all the four processes are long, two of them running peripherally and the others centrally; in some tripolar cells, one of the long processes runs peripherally and the other two centrally. In short, there are found multipolar cells that send out more than one long processes simultaneously running peripherally or centrally, in rather frequent cases.As a variation of multiform cells, I succeeded in proving the existence of fenestrated cells, though very sparsely, in the static ganglia of embryos in earlier stage