Histological Study of the Semilunar Ganglion of Dog

Abstract

The nerve cells found in the semilunar ganglion of the dog are classifiable into large cells and small cells by size, and by the number of their nerve processes into unipolar, bipolar and multipolar cells.The unipolar cells in the canine semilunar ganglion can be classified into the simple type and the complex type cells, as found in human ganglia, but many were found to show a specific type not observable in the human counterpart.Simple type unipolar cells are chiefly found among the small cells, and have single nerve processes which run very simple intracapsular courses before running out of the capsule. The unipolar cells of complex type are usually large cells and their nerve processes run spiral courses at one of the poles of the cells and then emerge from the capsule. Such unipolar cells with their processes running intricate courses surrounding the cell bodies, as often found in man, are only very rarely found in the semilunar ganglion of the dog.The specific type of the unipolar cells in the canine semilunar ganglion seems to represent a variation of the complex type. In a cell of this type, the nerve process sends out some rami during its spiral course, which run back to the mother fibre to form quite irregular-formed windows of varying sizes. Since similar cells are found in the spinal ganglia of horses too (LENHOSSEK), they are presumed to be present in the cerebrospinal ganglia of some non-human mammals.In nerve cells of any type, thick axis cylinders usually originate in large cells and thin cylinders in small ones, but exception are not rare. The axis cylinders of the unipolar cells divide into peripheral and central fibres by T or Y-shaped bifurcation, but no rule was found concerning their relative thicknesses. This applies also to the central and peripheral fibres of the bipolar and the multipolar cells equally well. The bifurcation of the axis cylinders of the unipolar cells generally occur without, but not rarely also within, the connective tissue capsules. The axis cylinders of the nerve cells of any type often send out thin collaterals.Bipolar cells too are found in the semilunar ganglion of the dog, though only in a very limited number. The formerly accepted theory that such bipolar cells represent infantile forms of unipolar cells has been refuted by YAMASHITA and MIKAMI of this laboratory, and my study also led me to deny such a hypothesis. The intracapsular courses of the two processes of such a bipolar cell are usually very simple in arrangement, that is, the cells are mostly of simple type, but sometimes, more complex-typed ones with spiral or fenestrated processes are found in existence.The multipolar cells in the semilunar ganglion of the dog are found in a larger number than in man, and in their formation, are sometimes quite dissimilar from those in the human ganglia. Namely, such common multipolar cells, simple fenestrated cells and nerve cells with endplates on their processes are very rare in the dog, but the majority of them consist in my so-called specific fenestrated cells with nerve processes running complex and peculiar courses.In such specific cells, their nerve processes emerge at varying distances on the surface of the cell bodies, come soon into mutual anastomosis to form a number of windows and then unite into single axis cylinders. These cells comprise those of simple and of complex types. In a simple-typed cell, the fenestration occurs at one of the poles of the nerve cells so that the formation is rather small and simple, but in a complex-typed cell, the nerve processes emerging at random distances from the cell surface make very variegated windows, before passing over into an axis cylinder generally running a winding course also peculiar to a cell of this type. Such specific multipolar cells of the simple type have been found also in the cerebrospinal ganglia of man and all other mammals