312 Anatomy of the Floor of the Fourth Ventricle 
lateral furrow, which connects the two, belongs to the acustic area. 
This area consists of a median, or vestibular field, and a lateral, or 
cochlear field. The vestibular field forms an irregular spindle shaped 
elevation, 16.1 X 4.5 mm., extending from the anterior fovea to the 
nucleus gracilis. Its median border is convex, and is more or less com- 
pletely separated from the nucleus intercalatus by the lateral furrow. 
In other mammalians (sheep and calf) this furrow of separation is more 
distinct than in man. The cochlear field is that portion of the floor 
that extends into the recessus lateralis. 
Lying near the median line, proximal to the striae medullares, and 
16 mm. cephalad to the obex, is a rounded elevation, + mm. in diameter, 
formed by the-genu of the facial nerve, inclosing the nucleus of the 
abducens. This we call the “eminentia abducentis.” Partly overlap- 
ping this, and extending forwards to the aqueduct of sylvius, is a longi- 
tudinal elevation, averaging 2.7 mm. in width. This is due to a field 
of grey substance consisting of fine fibres, in the meshes of which he 
scattered groups of small and medium sized multipolar nerve cells, 
which area begins as a thin layer in the region of the eminentia facialis, 
and gradually becomes thicker as it extends into the region of the 
mid-brain. Its function is wnknown, and we therefore call it the 
“nucleus incertus.” In its position it is closely related to the nucleus 
nervi trigemini, overlapping it throughout its course. 
Between the nuclei incerti, in the median line, is a shallow depression 
of the floor of the ventricle, measuring 5.7 K 1 mm. which forms the 
fovea mediana. The posterior longitudinal bundle here hes superficial 
in the floor covered only by a thin layer of ependyma. 
Lateral to the nucleus incertus, and the eminentia facialis is an elon- 
gated depression of the floor 3.2 mm. in its greatest width caudally, 
and gradually narrowing as it extends forward. It is due to the exit 
at this point of the root of the trigeminal nerve. It may therefore be 
called “* fovea trigemint” (anterior fovea). 
It may be hoped that familiarity with the facts pointed out in the 
above description will make more instructive the examination and dis- 
section of material from this region of the brain. 
In conclusion I wish to acknowledge my obligation and gratitude to 
Professor Edinger, at whose suggestion, and under whose guidance this 
work was done. 
Senckenbergisches anatomisches Institut, Frankfurt a. M. 
