If you are very fortunate, you may be able to see the
central canal of the caudal medulla and spinal cord as
it moves
rostrally and opens up under the cerebellum, becoming the 4th
ventricle (cerebrospinal fluid actually tends to run caudally
in the ventricular system). Under the rostral cerebellum, the
relatively thick anterior medullary velum should be easily
located, It forms the anterior roof of the 4th ventricle and
the rostral limit of the 4th ventricle is marked by the
attachment of the anterior medullary velum to the caudal
inferior colliculus. The 4th ventricle is continuous with the
cerebral aqueduct of the midbrain. Tissue dorsal to the middle
of the aqueduct is the tectum, and that ventral to its middle,
excluding the cerebral peduncles, is the tegmentum.
The tectum consists of the corpora quadrigemina and the
underlying lamina quadrigemina; the latter can be seen as the
cut surface immediately superior to the aqueduct, appearing
somewhat like the end of a piece of plywood (which is a
laminated structure). The cerebral aqueduct
opens up into the
3rd ventricle (discussed further in Plate 16) which in turn is
continuous with the two lateral ventricles that run out into
each cerebral hemisphere.