306 Anatomy of the Floor of the Fourth Ventricle 
and from Nissl and myelin sheath preparations are found to be devoid 
of nerve cells, axis cylinders, and blood vessels. The ependyma extends 
into the grey matter and median raphe in the form of processes, forming 
well defined partitions between the dorsal nuclei which Weigert, in his 
monumental work (Beitrige zur Kenntnis der Normalen Menschlichen 
Neuroglia), describes as “ kielstreifen,” or the tracks left by embryonal 
sulci. In adult specimens the place at which a process takes its origin 
is generally indicated on the surface of the ventricular floor by a more 
. Le or less well marked groove 
zee ee (text fig. 1). The size and 
form of the groove corre- 
spond in some degree to 
the size and compactness 
of the neuroglia process. 
‘That is: when the process 
is compact and slender the 
surface groove is usually 
sharply cut, and when the 
process is broader and less 
Fasc. solitar. compact the surface de- 
Text Fia@. 1. Section showing the distribution of the 
neuroglia fibres in the floor of the fourth ventricle ata pression is shallower and 
level corresponding to fig. 5, Plate III. The drawing 
represents the appearance as seen under low magnifica- More rounded out. Ow- 
asc ing to this partition for- 
mation it is possible with low magnification to make out in glia fibre 
preparations the definite boundaries of the dorsal nuclei. So we have, 
in the comparison of these specimens with myelin sheath and Nissl 
preparations, another means of determining the size and arrangement 
of the dorsal nuclei. 
In fig. 5, by comparison with text fig. 1, it is easy thus to determine 
that the three major areas are occupied by the vestibular, vagus and 
hypoglossal fields. We further see that the hypoglossal field is subdi- 
vided, and that the lateral subdivision (area plumiformis) corresponds to 
the “nucleus intercalatus ” of Staderint and Van Gehuchten (Van Ge- 
huchten—Recherches sur Vorigine réele des nerfs craniens. III. Le 
nerf glosso-pharyngien et le nerf vague. Journal de Neurologie 1898- 
1899), which nucleus forms a dorso-lateral cap over the hypoglossal 
nucleus. The hypoglossal nucleus, itself, appears in the floor of the 
ventricle only in the median division of the trigonum. We find that 
it is the prominenee of the hypoglossal nucleus and small development 
of the nucleus intercalatus that results in the rounded surface elevation 
called eminentia medialis trigoni by Retzius (Eminentia hypoglossi, 
Plates I and JT). 
Nucl. intercalatus 
Nucl. Vagi 
Nuel. hypoglossi 
