On Various Nuclei of Vagal and Glossopharyngeal Nerves in Cat Brain

Abstract

In cat as well as in man, the nucleus calami scriptorii can be demonstrated in the subependymal layer of the calamus scriptorius. Its size and form, however, are considerably dissimilar from that in man, owing to the difference in the form of the entire brain stem. In man, the cross-section of this nucleus is of oval form elongated ventrodorsally at the height of the obex, but in cat, it is an isoscele triangle elongated transversely, with its apex oriented toward the median line. In size, the nucleus is even larger than in adult man, showing a powerful development. This nucleus bends lateralwards in the range above the obex and reaches the point where the fossa rhomboidea grows to the breadth of 3mm, that is, 3 times as far lateralwards as that of man, before ending. On the levels lower than the obex, it loses rapidly in size, turns more medialwards and fusing with the same nucleus of the other side, soon terminates.This nucleus is not merely a promontorium gliosum consisting of glial tissue, but is a separate nucleus, since many small nerve cells are found in the glial tissue. Each of these nerve cells contains a comparatively large oval or round cell nucleus containing in turn one conspicuous nucleolus. Hard-stainable neurofibrils are seen in its cell body and the nerve processes emerging thence are also hard to stain, while its single axis cylinder gathers with other similar cylinders into small bundlets and runs through the undermentioned nucleus rotundus and nucleus dorsalis microcellularis finally into the tractus solitarius. In this nucleus of cat, melanin pigment cells, that have been discovered in the human counterpart, were not observed.In transverse sections at the height of the obex is visible the nucleus dorsalis on the dorsolateral side (on the dorsal side in man) of the nucleus hypoglossus separated from the latter by the nucleus intercalatus. This nucleus consists of the nuclei dorsales macrocellularis closed to the dorsal part of the intercalatus and microcellularis lying on the dorsal side of the former.The cross-section of the macrocellularis is of oval form elongated transversely and in area approximately equals that of the nucleus hypogloseus on the same level. The number of large nerve cells found in a section at the height of the obex is about 90 or about 3.5 times as large as that of the human nucleus, but diminishes rapidly as we go down from the height of the obex and ends caudally on the same level as the hypoglossus. On the levels higher than the obex, its major axis of cross-section runs from the dorsomedial to the ventrolateral. The number of cells per section temporarily increases, but soon begins to decrease gradually, falling to around 60 at the height of the cranial end of the nucleus calami scriptorii. In the higher range, the nucleus is found transposed to the medial of the tractus solitarius and fades out at the height where the hypoglossal nucleus goes out.In this nucleus, no pigment cells are contained, though a small number of small nerve cells are detected. The large nerve cells show no such perceptible local difference in size in cat as in man (KOMATSU), are spindle-form or polygonal, are one-third or half as large as the motor cells in the hypoglossus, show rounded contour dissimilar to that of motor cells, contain hardly stainable nerve fibrils and send out thick dendrites which often branch out and perhaps end in sharp points. It seems that fine vegetative fibres from the formatio reticularis end in relation to these dendrites. The neurites from the cells are thin but rather dark-staining, and gathering together into bundlets, run into the solitary tract through the microcellular nucleus. The small nerve cells also show similar nature, and it is certain these nerve cells are all of vegetative nature. Some dark-staining thick fibres are also found in this nucleus, which are probably sensory fibres playing a part in the reflex function.