302 Anatomy of the Floor of the Fourth Ventricle 
review of the subject. It is a curious fact that, as the anatomies be- 
come more modern, the descriptions and illustrations of this part of 
the nervous anatomy correspond less and less to nature, and drift toward 
misleading multicolored diagrams. Retzius points this out, and pro- 
duces a page of drawings taken from different sources showing a lament- 
able lack of faithfulness on the part of the more modern writers. 
Stimulated by this, Retzius makes a careful study of one hundred 
specimens, and illustrates the typical forms with drawings and well 
executed photographs. His description of the floor of the fourth ven- 
tricle is so complete that we cannot do better than to follow it more 
or less in detail: 
The ventricular floor, in the majority of cases, is divided by the striae 
medullares into three regions, namely: ‘The “frontal,” the “ median ” 
(a region occupied by the striae), and the “ caudal.” The striae, how- 
ever, as is well known, present a great individual variation. They may 
be large, small, or entirely absent. When present they le parallel, 
convergent, divergent, transverse, oblique, or longitudinal. Owing 
to this irregularity, Retzius agrees with His in recommending, for de- 
scriptive purposes, a longitudinal division of the floor,—each side to 
be divided into a median and lateral area, which is indicated by a more 
or less well marked groove connecting the superior and inferior (ala 
cinerea) foveae. ‘This groove is called the “lateral furrow,’ and the 
foveae are merely parts of it widened out. Such a groove in a gross 
way separates the motor and sensory fields of the floor of the ventricle, 
the former of the two lying mesial. In adults’ brains at the caudal tip 
of the ventricle (calamus scriptorius) there is usually present a small 
triangular bridge-like structure (obex), extending between the promi- 
nent nuclei of the posterior columns of the cord (clavae), and covering 
in the tip of the ventricle in the median line. Arising from under this 
and out of the opening of the central canal and extending from the 
median line along the edge of the clava is the “Area postrema,”’ a 
rounded tongue shaped space with a fine granular surface and brownish 
color. This area was already known to Stilling and Henle, but is espe- 
cially described by Retzius. Two other structures come out with this 
from the region of the central canal, the ala cinerea and, next to the 
median line, the hypoglossal field or the trigonum hypoglossi. The area 
postrema is distinguished from the ala cinerea by its color, rougher sur- 
face, and by a glistening light colored ridge, which separates the two. 
This ridge is usually well marked, and extends laterally and anteriorly 
to the inferior end of the area acustica, in the structure of which it is 
lost. From its position Retzius names this ridge the “ Funiculus 
