yeorge L. Streeter 301 
rations stained in various ways, including a series of neuroglia fibre 
specimens prepared by Weigert, and kindly loaned for this purpose. 
Before giving the results of the study of these preparations we will 
briefly review that which has already been found out concerning the 
anatomy of the ventricular floor. 
Stilling, sixty years ago, in describing the floor of the fourth ventricle, 
divided the caudal half of it, on each side of the median line, into three 
triangles (Bau des Nervensystems, 1842). One of these, the “Ala 
cinerea,” owing to its darker color, stands out prominently, its apex 
extending forward to the “ transverse fibres of the acustic nerve,” and 
its base resting against the “Calamus scriptorius.” This he deter- 
mines to be the nucleus of the vagus nerve. He observes a small 
ridge running across the base of this triangle, cutting off a distal seg- 
ment, and so separating the anterior part, or “ Vagus nucleus,” from 
the caudal border of the ventricle. The posterior segment he names 
“Nucleus of the Accessorius ” (Stilling, Taf. VII, fig. 9). The other 
two triangles, separated by the ala cinerea, lie with their apex directed 
backwards. The median one is his “ Hypoglossal nucleus,” and the 
one lateral to the ala cinerea he calls the “ Nucleus of the Glosscphar- 
yngeus.” In the anterior division of the floor of the ventricle, Arnold 
had previous to Stilling described the “ Eminentia teres,” the “ Fovea 
anterior,” and “ Locus coeruleus.” The first of these Arnold had identi- 
fied as the “ Nucleus nervi facialis ” (Icon. nerv. cap. Taf. I, fig. 8). He 
also describes the “Striae medullares” and suggests their association 
with the auditory nerves. 
That much, then, was found out regarding the floor of the fourth 
ventricle, without the aid of any imbedding or staining methods, and 
from sections cut with a razor. 
A quarter of a century later J. Lockhart Clarke (Phil. Transact., 1868, 
p- 263), from specimens stained with carmine and cleared in the oil of 
turpentine, concludes that the triangle lying lateral to the ala cinerea 
is the “inner nucleus of the auditory nerve.” He also makes out the 
course of the facial nerve with its knee and two arms. He considers 
its nucleus of origin to be situated beneath the fasciculus teres, in com- 
mon with that of the abducens. The loose strands of the posterior arm 
he describes as an association bundle between the facial and the motor 
nucleus of the trigeminus. 
From this time until Retzius published his work on the “ Menschen- 
hirn,” in 1896, we find no important contribution to our knowledge of 
the floor of the fourth ventricle. Henle’s work (Nervenlehre des Men- 
schen, 1879) should perhaps be mentioned as giving the most careful 
