Human Embryo
Al-4
In the human embryo identify the large
telencephalic vesicles and the choroid plexus. The
cavity in these (the lateral ventricles)
communicate with the ventricle of the diencephalon
(3rd ventricle) through the interventricular
foramen
A3:
inside the lateral ventricle
Al-2:
Distinguish the wall of the forebrain.
A3-4:
The basal part of the telencephalon forms the basal
ganglia, a solid mass. Posteromedially these basal
ganglia are in contact with the diencephalon. The
large masses in either side of the diencephalon
form the thalami.
Al-7,
B1: The diencephalon. In these levels the
brain comes into section twice, because of the
cephalic flexure, but in A2-4 the two parts are
connected.
Al-5:
Ventral to the thalamus you can identify the
hypothalamus.
A6-7,
B1: The hypothalamus
A6:
the lamina terminalis, original anterior end of the
neural tube. Notice the position of the optic
nerves in relation to the hypothalamic part of the
diencephalon (B1).
B2-3:
Further caudally the pituitary gland is seen, the
neural part of which is a derivative of the
diencephalon.
Al-7:
The midbrain (mesencephalon). Its dorsal part is
the mesencephalic vesicle, a large, thin-walled
structure (A2-6) which overlaps the initial part of
the metencephalon (A6-7).( The ventral part of the
mesencephalon is seen to be continuous with the
diencephalon in A3-4. The tectal recess, an
extension of the roof the mesencephalic vesicle is
seen in A6.
A6:
The junction between the mesencephalon and
metencephalon is called the isthmus. The main
metencephalic derivatives are the pons and
cerebellum.
The ventricular lumen of the hind brain is the
4th ventricle (A7, B1-7, C1-3). The roof of the
metencephalic part of the 4th ventricle is formed
by the developing cerebellum (B2-3), beyond which
the ventricle forms two large lateral recesses
(B2-3). In more caudal sections the roof of the
ventricle is seen as a thin membrane only, bearing
choroid plexus.
B2-3:
the root of the trigeminal nerve and its
ganglion.
The myelencephalic part of the hind brain will
form the medulla oblongata, the embryonic
appearance of which is hardly different from the
fully developed structure. The vagus nerve and its
ganglion are seen to leave the base of the brain in
B7, through the jugular foramen.
At all levels where the brain is present notice
the meninges enveloping it and creating the large
subarachnoid space which is filled with
cerebrospinal fluid.
Study the histological appearance of the spinal
cord. Note the alar and basal laminae, the dorsal
root ganglia and the sympathetic trunk.
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