300 Anatomy of the Floor of the Fourth Ventricle 
structures which he describes as forming a part of the floor of the fourth 
ventricle, and their relation to the underlying parts. 
Since now we know, after many investigations, so much concerning 
the finer structure of the oblongata, and also have from Retzius such an 
accurate description of the surface, what a tempting task is offered in 
the study of the relation of the one to the other! A more complete 
knowledge of this relation, it may indeed be hoped, will render the 
understanding of the structure of this complicated region somewhat 
easier. 
The simple plan was adopted of making a drawing of the floor of the 
ventricle, and then preparing from the same specimen a series of trans- 
verse sections taken at recorded levels. An adult brain was selected 
which had been hardened in formaline and showed distinctly the various 
structures in the ventricular floor. Regard was given to the fact that 
some variation exists in the arrangement of the markings in different 
brains. A specimen was therefore selected that showed best the more 
constant arrangement. <A drawing of this was then made, the specimen 
being carefully studied under water and the finer structures brought 
out with a simple lens. Each part was measured as accurately as pos- 
sible and reproduced in the drawing enlarged twice. This is shown 
in Plate I. Photographs and tracings were then made from the drawing 
to serve as duplicates, for purposes of additional record. The specimen 
was then cut transversely into measured segments, either 2 or 4 mm. 
thick, varying according to the complexity of the region, the level of 
the segments being recorded on a duplicate of the drawing. By recon- 
structing the specimen after section it was possible to see exactly 
through what parts the incisions were made, and so a control record of 
the levels was kept. The segments were then mordanted preparatory 
to the myelin sheath method, imbedded in celloidin, and cut. During 
this process there was some warping of the segments, so that in trimming 
on the microtome the final sections were in some cases not exactly 
transverse. Such corrections were recorded. The first sections taken 
from the blocks were kept apart, as corresponding to the recorded levels 
on the drawing; the deeper ones were preserved as a series for purposes 
of identification. The sections, thus prepared, were stained by Wei- 
gert’s myelin sheath method. Some of the more important ones are 
reproduced in Plates III and IV, the enlargement being twice that 
ased in the drawing of the floor of the ventricle, 7. e. four times natural 
size. The levels corresponding to the sections are indicated on Plate II. 
For accuracy in identification of structures, comparison was made with 
other series, taken from the collection of the Institute, and with prepa- 
