At the position corresponding to the subependymal layer of the calamus scriptorius, I have found a nucleus which I propose to call the nucleus calami scriptorii. This nucleus contains in its loosely arranged glial tissue small nerve cells and, especially in pits medial parts, some larger melanin pigment cells, both with very fine axis cylinders which, forming small bundlets, run through the undermentioned nuclei rotundus and dorsalis microcellularis, to pass over into the fine vegetativa fibres in the tractus solitarius. This nucleus becomes gradually worse developed as the fossa rhomboidea passes over into the canalis centralis. It is first located on the dorsal side of the canalis and its right and left halves are bounded by a narrow raphe of glial tissue, but soon they become fused in one. Some decussating bundlets are demonstrable therein.
In a transverse section of the brain stem at the height of the obex, we see a broad band of grey substance dorsal to the nucleus hypoglossus and between the snbependymal layer and the nucleus calami scriptorii on the one hand and the tractus solitaruis on the other, half-surrounding this tract on the dorsomedial side. This band has been long named the nucleus dorsalis. In this nucleus, however, I could distinguish a group of large nerve cells on the dorsal side of the hypoglossal nucleus and extending from the dorsomedial to the ventrolateral, which I propose to name the nucleus dorsalis macrocellularis. The number of the large nerve cells in this group averages 25 in a transverse section on the level of the obex and decreases thence caudalwards, falling to nought on a level somewhat below the caudal end of the hypoglossal nucleus. Upon reaching a level more cranial to the obex, it begins to move to a more dorsal position, and when the ala cinerea comes into view, it takes up a position dorsomedial-ventrolaterally bridging the hypoglossal nucleus and the solitary tract, on the lateral side of the subependymal layer in this part and here the cells number from 35 to 45. At the topmost level of the calamus scriptorius, the group attains the maximum development and consists of 65-75 nerve cells in one section. But ascending further to the fevel where the ala cinerea begins to narrow down, its development also falls off, and when the nucleus triangularis begins to protrude into the fossa rhomboidea, the nerve cells begin to move into the deeper parts. They come into contact with the formatio reticularis midway between the tractus solitarius and the hypoglossal nucleus here and soon are lost sight of altogether. Near the end of this group, many thick motor fibres from the nucleus ambiguus are found meandering among the now extremely decreased nerve cells. The level where this nucleus ends cranially is somewhat higher than the cranial end of the nucleus hypoglossus and somewhat lower than that of the tractus solitarius.
A small number of small nerve cells is also contained in the nucleus dorsalis macrocellularis. Its large cells are larger in thigher than the lower parts and larger in the dorsal than in the ventral parts. These are, however, always smaller than somato-motor cells, and are different from the latter in form too, showing rounded, and not the rugged contour of the latter. They are variously shaped spindle-like, round, oval, or polygonal. Their intracellular nerve fibrils are very fine and only weakly stainable, and this characteristic also, coupled with the comparatively large size of their nuclei, serves in distinguishing them from sensory and somato-motor cells, and clearly indicates that they are of vegetative nature. The small nerve cells are only smaller in size, but are of the same nature too.
The dendrites of the nerve cells, and especially those of the large cells, are thick and long and seem to end in sharp points after ramification. Accompanying these cells and their dendrites, we often find fine but strongly stainable nerve fibres.