310 Anatomy of the Floor of the Fourth Ventricle 
the central canal of the spinal cord, in which Onuf and Collins (Experi- 
mental researches on the central localization of the sympathetic. Archiv. 
Neurol. and Psychopath., 1900) have traced secondary degenerations 
following removal of sympathetic ganglia. 
CONCLUSION. 
Now, that we have examined our series individually, we are in a 
position to consider the floor of the ventricle as a whole, and the posi- 
tion and arrangement of the structures of which it consists. The fact 
that we have the levels of the sections exactly recorded enables us to 
plot out the areas of the various nuclei and tracts, as far as we were 
able to identify them in section. Further, as all the drawings were 
enlarged according to a definite scale, we are enabled to give their exact 
size in length and width. In Plate II the different areas have in that 
way been outlined. If we compare this plate with the original drawing 
(Plate I), we can see the relations of the outlined areas to the super- 
ficial structure of the floor. As a résumé, therefore, that which we see 
in the floor of the fourth ventricle, when looking at our specimen from 
above, and taking in consideration but one side of the median line, may 
be described somewhat as follows: 
Lying against the median line in the caudal half of the floor is an 
oval elevation, 5.2 < 1mm. This represents the rounded frontal end of 
the hypoglossal nucleus, and may therefore be called “ eminentia hypo- 
glossi” (eminentia medialis trigoni of Retzius). It varies somewhat in 
prominence in different specimens according to the development of the 
structures lateral to it. In the specimen illustrated in Plate I it is 
less prominent than is usual. The remainder of the hypoglossal nucleus 
is completely covered by. other structures. The entire nucleus meas- 
ures 12.38 X 2.2 mm. The intraventricular portion is 7 mm. long, and 
except at the eminentia hypoglossi is overlapped by the nucleus inter- 
calatus and nucleus vagi. The extraventricular portion extends 5.3 mm. 
caudad to the tip of the calamus scriptorius, and lies ventral to the vagus 
nucleus and the nucleus of the funiculus gracilis. 
Situated at the median line frontal to the eminentia hypoglossi, and 
separated from it by a slight depression, is a somewhat similar, but less 
prominent, elevation formed by the nucleus funiculi teretis. This 
measures 5.7 X 1mm. The appearance of this structure varies accord- 
ing to the arrangement of the striae, which have their median termina- 
tion in this region. It is possible that there is an intimate relation 
between the striae and this nucleus. 
