Книги по МРТ КТ на английском языке / The Embryonic Human Brain An Atlas of Developmental Stages. Third Edition. 2006. By Ronan O'Rahilly

Figure 24–3. 33 mm. Projection of diencephalic tracts. The entrance of the Stammbundel¨ (Fig. 24–2) has not been included. The dorsal thalamus (stippled) takes up almost half of the medial surface. Some of the diencephalic nuclei are shown (hatched). The subthalamic and entopeduncular nuclei, and the globus pallidus externus, are clearly identifiable but have not been represented in the reconstruction. The preoptico-hypothalamotegmental tract is indicated by a dagger. The accessory optic tract ends in the region of the subthalamic nucleus, as described by Gilbert (1935) and Cooper (1946b), although the fibers in the adult are connected to the mesencephalic lateral and dorsal terminal nuclei (Fredericks et al., 1988).

Figure 24–4. 33 mm. Schematic presentation of the inferior olivary nucleus. In addition to the accessory olivary nucleus (medial to the hypoglossal nerve) and the principal olivary nucleus (lateral to the hypoglossal nerve) seen in stage 23, further subdivisions can now be distinguished: (1) the medial accessory olivary nucleus, a rostral part with tall cells; (2) a mediocaudal portion consisting of medium-sized cells related to internal arcuate fibers; (3) probably the caudal medial accessory nucleus, a group between the first two and containing small cells;

(4) probably the dorsal accessory nucleus, situated dorsolaterally and containing small cells; and (5) the main nucleus, the most voluminous part, which consists of tall cells. Projections to the cerebellum were present already in stage 23 (Fig. 23–30D). The olivocerebellar fibers join the inferior cerebellar peduncle. In cross sections the olivo-arcuate migrating cells are seen as superficial and intermediate strands, and the cellular axes are arranged tangentially.

C-Shaped Structures

A B

1

2

3

4

C

1

2

3

4

Figure 24–5. Associated with the growth of the relatively fixed corpus striatum and the expansion of the cerebral hemispheres in a curved direction to form the temporal lobes, a number of structures develop in a C-shaped manner: (A) the caudate nucleus (head, body, and tail); (B and C) the choroid plexus and the choroid fissure through which it passes; the fornix (columns, body, and crura) and its continuation, the fimbria; the hippocampus and dentate gyrus, the rostral portions of which are found later merely as a remnant termed the indusium griseum;

(C) the corpus callosum, which halts (as the splenium) without descending into the temporal lobe.

Central part

D

E

Parahippocampal gyrus

Figure 24–6. C-shaped structures (Continued ). (D) the lateral ventricle (anterior horn, central part, and inferior horn); (E) the limbic lobe (cingulate and parahippocampal gyri); and the frontal, parietal, and temporal lobes of the hemisphere.

Figure 24–7. 33 mm. Lateral view showing the ventricles. Some recesses are well formed, e.g., the supramamillary and the inframamillary, whereas others, e.g., the suprapineal, are not clear. The long cavity of the isthmus is narrowing because of the growth of the cerebellum, but it still extends into a well-developed isthmic recess.

TABLE 24–1. Important C-Shaped Structures in the Brain

Figure 24–10. 27.5 mm. The corpus striatum, internal capsule, and adjacent structures. The claustrum is well developed, and a clear connection with the ventricular layer of the olfactory area still exists (Fig. 24–15). The external capsule has appeared. Fibers of the internal capsule are seen to reach the diencephalon through the hemispheric stalk, which is delimited by the sulcus terminalis.

The key drawing shows the area included in the photomicrograph. The arrival and origin of the fibers in the subplate are depicted. The ventricular eminences are said to expand to about 10 times the maximum thickness observed in other regions of the CNS during the second month, but reach their peak only at the middle of prenatal life (Rakic and Sidman, 1982). Their growth is supported by the striatal arteries (Nelson et al., 1991), which mature earlier than the arteries of the cerebral wall, that is, they develop a muscularis between 20 and 22 weeks. The ventricular layer contains a network of vessels that possess no muscularis at any age. The regression of the ventricular layer is accompanied by a regression of the capillaries (Nelson et al., 1991).

Figure 24–11. 27.5 mm. An enlargement of the internal capsule at a more dorsal level. The key drawing is a graphic reconstruction.

Internal

capsule Subplate

Cortical plate

Figs 24 – 15 13 11

Figure 24–12. 27.5 mm. The hippocampus is clearly recognizable because of its thinner ventricular layer, which is contiguous to the lamina epithelialis. The third ventricle is visible below, and its folded roof seems to show the beginning development of choroid villi. The thick fiber bundle on each side of the roof area is the stria medullaris thalami. The choroid plexuses of the lateral ventricles are well shown.

Presubiculum

Hippocampus

Figure 24–13. 27.5 mm. The hippocampus more ventrally has joined the prosencephalic septum. The hippocampal sulcus has appeared and is contiguous to the rhinal sulcus, as shown in the key drawing with Figure 24–11. The falx cerebri is evident. The lateral ventricles are seen to be continuous with the cavity of the telencephalon medium, which in turn blends with the third ventricle between the thalami. See also Figure 24–10. The sulcus

Hippocampus terminalis lies between the ventricular eminence and the dorsal

thalamus.

Lamina terminalis

l.-v.f.

Sulcus terminalis