Development during the fetal phase
Over the course of the fetal phase the neopallium experiences considerable expansion at the expense of the archipallium and palaeopallium.
In this, the hemispheres gradually grow around the diencephalon. Through the strong proliferation of the amount of striate bodies, a thickening in the connection region between the telencephalon and diencephalon occurs so that these two parts merge into one another over large areas. The portion of the meninges that then still lie between the two brain sections atrophy and a fusion of the hemisphere floors with the thalamus takes place.
The broad connection zone permits the entry of nerve fibers that connect the hemispheres with the other segments of the nervous system. The white matter in the stem region appears as the internal capsule.
Lamina affixa: adhesion location between ependymal layer of the ventral segment of the hemisphere vesicles and the dorsal area of the thalamus. This region then becomes the floor of the central part of the lateral ventricles between the stria terminalis and the taenia choroidea.
- 1
- Location where the diencephalon is covered by the expansion
of the cerebral hemispheres - 2
- IIIrd ventricle
- 3
- Hypothalamus
- 4
- Thalamus
- 5
- Pallidum
- 6a
- Body of the caudate nucleus
- 6b
- Tail of the caudate nucleus
- 7a
- Choroid plexus in the lateral ventriclel
- 7b
- Choroid plexus in the IIIrd ventricle
- 8
- Pallium
- 9
- Lateral ventricle
- 10a
- Cortex of the dorsal hippocampus
- 10b
- Cortex of the ventral hippocampus
- 15
- Inferior horn of the lateral ventricle
- 17
- Choroid fissure
As can be recognized in this cross section caudal to the interventricular foramen (see sectional plane B) at around the 11th week the hemisphere vesicles grow together with the diencephalon.
Note the transition from the hemispheres to the roof of the diencephalon (choroid fissure). Through the horseshoe-shaped expansion of the hemispheres certain structures near the ventricle are relocated into the temporal lobes.
- 1
- Fusion region between the diencephalon and the telencephalon
- 2
- IIIrd ventricle
- 3
- Hypothalamus
- 4
- Thalamus
- 5
- Pallidum
- 6a
- Body of the caudate nucleus
- 6b
- Tail of the caudate nucleus
- 6c
- Putamen
- 6c
- Claustrum
- 7a
- Choroid plexus in the lateral ventriclel
- 7b
- Choroid plexus in the IIIrd ventricle
- 8
- Pallium
- 9
- Lateral ventricle
- 10a
- Cortex of the dorsal hippocampus
- 10b
- Cortex of the ventral hippocampus
- 15
- Temporal horn of the lateral ventricle
- 16
- Lamina affixa
- 17
- Choroid fissure
At a still later time, a cross section caudal to the interventricular foramen (see sectional plane B) reveals the considerable expansion of the neopallium as well as the adhesion between the hemisphere floor and the roof of the diencephalons in the form of the lamina affixa. The already extensive differentiated striate bodies are forced to the side.
- 1
- Fusion region between the diencephalon and the telencephalon
- 2
- IIIrd ventricle
- 3
- Hypothalamus
- 4
- Thalamus
- 5
- Pallidum (medial striatum)
- 6a
- Body of the caudate nucleus
- 6b
- Tail of the caudate nucleus
- 6c
- Putamen
- 6d
- Claustrum
- 7
- Choroid plexus of the lateral ventricle
- 8
- Pallium
- 9
- Lateral ventricle
- 10a
- Cortex of the dorsal hippocampus
- 10b
- Cortex of the ventral hippocampus
- 11
- Insular cortex
- 12
- Amygdala
- 13
- Corpus callosum
- 14
- Fornix
- 15
- Temporal horn of the lateral ventricle
- 16
- Capsula interna
Cross section through the prosencephalon at the level of the interventricular foramen (see sectional plane A). In this advanced stage the diencephalon, through the massive expansion of the hemispheres, is extensively grown over (dotted green line). Through the horseshoe-shaped growth of the hemispheres certain structures near the ventricles are relocated together into the temporal lobes. With the formation of the lateral sulcus, the insular cortex is slowly covered over in the depths.
Out of the lateral neostriatum, lying on the floor, arise the caudate nucleus and the putamen in the course of the further development. In contrast, out of the medially lying palaeostriatum of the diencephalon emerges the globus pallidus (in short: pallidum). Macroscopically this, together with the putamen, is summarized as the lentiform (or lenticular) nucleus. The amygdala or archistriatum finally develops ventrally to the lentiform nucleus and apparently derives from the diencephalon and the telencephalon.