Histological Investigation of Nucleus Facialis of Cat

Abstract

The group arrangement of nerve cells in the facial nucleus is simpler in cat than in man, the groups being divisible only into a larger inner and a smaller outer group even at the medial part. The latter can be subdivided into the ventral and the dorsal subgroups. Any attempt at further subdivision would lead to inappropriate results.The inner group, in a transverse section of the brain stem, is approximately circular in outline, its circumference being surrounded by minute fibres, though not completely. These fibres pass over into the trellis works of the formatio reticularis on the dorsal and the medial sides and of the tractus spinocerebellaris ventralis and the tractus tectospinalis on the ventral side. The dorso-lateral subgroup is formed by nerve cells buried in an extension of the trellis work of the formatio reticularis and is also circular. The ventrolateral subgroup has the form of an oval elongated laterally and is surrounded by fine fibres, which come in connection with the trellis works of the tractus rubrospinalis and of the tractus tectospinalis.The motor nerve cells in the facial nucleus of cat are generally in comparatively dense arrangement and 30-40μ in size. They send out 6-10 nerve processes per cell, between which the outlines are concave, giving a rugged and masculine appearance to the cells. Thus, these may be easily distinguished from the rounded feminine looking sensory nerve cells as in the trigeminal sensory nucleus.The processes from these nerve cells are always smooth-surfaced. The long processes or the axis cylinders are much finer but more dark-staining than the short processes, and some cells send out two or one bifurcated axons. The short processes are very thick and stout, but their nerve fibrils are very weak-staining, and branch out and end in sharp or blunt points without losing much of their thickness throughout their long courses.The cell nucleus of the motor nerve cell is situated at the center of the cell body, is round-shaped and contains rather meagre chromatin and a weakly-staining round nucleolus. No pigment granulae were found in the cell bodies, as were found in human motor cells.The facial nucleus of cat contains, beside the motor nerve cells, a comparatively large number of small nerve cells, especially numerous in the dorsal and the medial parts of the inner group. These are rather variable in form, have only a few processes per cell and often show the appearance of being apolar. Their cell nuclei are placed eccentrically and are formed similar to the cell bodies in which they are found, contain much chromatin and number also one per cell, are smaller than those of the motor cells above, but look rather oversized for the cell bodies. Similar small cells are also found in the minute fibres surrounding the facial nucleus and the trellis-works of the formatio reticularis on the outside of the former and are presumed to be centers of salivation, so that we may take the small cells in the facial nucleus to have the same function too.Beside the above, the facial nucleus, in particular, the dorsal part of its inner group, contains nerve cells of a size similar to that of the motor cells, but having a more rounded profile and with a little fewer processes per cell than the latter. Cells of such a type belong to the sensory nerve cells in the brain stem and consequently, we might assume that a part of the fibres of n. intermedius terminates in the facial nucleus.As the incoming fibres supplying the facial nucleus of cat we may first enumerate the fibres from the trigeminospinal tract, which run right through or along the dorsal side of the nucleus infratrigeminalis into the formatio reticularis and thence finally to the facial nucleus. Next, we may refer to the acoustic fibres, which run into the facial nucleus of the same side from its ventrolateral side before reaching their destination in the nucleus trapezoides.