. The Journal of comparative neurology and psychology. fibers of this root. The same has been clearly demonstratedin sections of the sturgeon ])rain not used for the previous study. The origin of the fibers has been seen in the toad and will be de-scribed in the following section. In the rat, mouse and rabbit theyhave been studied in sections prepared by the Cajal and Eielschowskysilver methods, and it need only be said that the description by Cajalis confirmed (Figs. 4 and 5). 6o2 Journal of Comparative Neurology and Psychology. 2. The Position and Character of the Cells of Origin.—In allfish
. The Journal of comparative neurology and psychology. fibers of this root. The same has been clearly demonstratedin sections of the sturgeon ])rain not used for the previous study. The origin of the fibers has been seen in the toad and will be de-scribed in the following section. In the rat, mouse and rabbit theyhave been studied in sections prepared by the Cajal and Eielschowskysilver methods, and it need only be said that the description by Cajalis confirmed (Figs. 4 and 5). 6o2 Journal of Comparative Neurology and Psychology. 2. The Position and Character of the Cells of Origin.—In allfishes and amphibians studied the cells of origin are located in thetectum mesencephali, the majority of them near the median are always massed along the median line without apparentbilateral symmetry or any other regularity of arrangement. In theselachians they are often piled two or three deep at the median they form a single row or are scattered, an occasionalcell being found at the extreme border of the proper roof portion. Fig. 4. Cells of origin of the radix mesencephalica in the locus coeruleus ofthe rat. A is farther mesad and cephalad; B, farther caudad and B two cells send their processes caudad (toward the left). of the tectum (Fig. 6). In Scyllium and Squalus they extendthroughout the entire length of the tectum and the greatest numberof cells is found at the posterior part of the tectum. In Scylliumstellare there is an especially large group which extends into themedullary velum so that several cells lie beneath and behind thecrossing fibers of the IVth nerve. In Acipenser the cells are to befound only in the anterior part of the tectum, the majority of themin the immediate vicinity of the posterior commissure (Johnston,1901). In Araia embryos and young up to 25 mm. in length, the Johnston, The Radix Mesencephahca Trigennni. 603 cells have the same position. In the youngest embryo that I havestudied the cells are seen in the thin p
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