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

Stria medullaris thalami

Habenulo-interpeduncular tract

Lateral habenular nucleus

Figure 19–13. The lateral habenular nucleus in a sagittal section, an example of a far-advanced epithalamic area. The arriving fibers are of the stria medullaris thalami, the leaving fibers form the habenulo-interpeduncular tract (Fig. 19–23).

162 C h a p t e r 1 9 : CHOROID PLEXUS OF THE FOURTH VENTRICLE AND THE MEDIAL ACCESSORY OLIVARY NUCLEUS

Figure 19–17. A sagittal section to show the epiphysis, which is now a rostrally directed outgrowth of the roof of the synencephalon (Fig. 19–16D). This is the Vorderlappen of Stadium IV of Turkewitsch (1933). It projects towards the left side of the photomicrograph and forms a characteristic “step” (Stufe). Two so-called follicles are visible, as observed also by Hochstetter (1923). The site of the epiphysial evagination is marked by the pineal recess. Bar: 0.05 mm.

Figure 19–18. The terminology of the hypophysis cerebri based on

Rioch et al. (1940). Cf. Table 17–2.

164 C h a p t e r 1 9 : CHOROID PLEXUS OF THE FOURTH VENTRICLE AND THE MEDIAL ACCESSORY OLIVARY NUCLEUS

Mes. tract of 5

Inf. cerebellar peduncle

Figure 19–20. The area of the pontine flexure with cranial nerves 5, 7, 8, 9, and 10, silver-impregnated. Many tracts are identifiable, e.g., the mesencephalic tract of the trigeminal nerve, the trigeminospinal tract, and the tractus solitarius. Among the cerebellar connections are found the inferior cerebellar peduncle (vestibulocerebellar and trigeminocerebellar fibers) and even components of the superior peduncle (dentatorubral fibers, which pass lateral to the nucleus isthmi). The porus duralis of the trigeminal nerve is visible. The internal carotid artery, sectioned below the trigeminal ganglion, is filled with blood and possesses a thick arterial wall. Bar: 0.2 mm. From Muller¨ and O’Rahilly (1990a).

In monkeys at a comparable stage, cerebellar neuronal production is at a peak. Two migratory waves participate in the formation of the cerebellum: from the rhombic lip, the migrating cells being at the surface, to which their nuclei are parallel; and from the ventricular layer, the cells lying at a right angle to the surface of the cerebellum. The cells of the two migrations become partly mixed, as is true in the dentate nucleus.

Parasympathetic ganglia appear in the head between stages 15 and 19 (Wozniak´ and O’Rahilly, 1980).

Inferior cerebellar peduncle

Trigeminospinal tract

Figure 19–21. The cochlear nerve and nuclei. The cochlear nerve has a spiral pattern like a rope from stage 19 onwards. It pierces a dense mass of cells (the ventral cochlear nucleus), where it enters the rhombencephalon. Both cochlear nuclei are lateral to the inferior cerebellar peduncle, whereas the vestibular nuclei are medial. An asterisk indicates the tractus solitarius in the key. Bar: 0.1 mm.

166 C h a p t e r 1 9 : CHOROID PLEXUS OF THE FOURTH VENTRICLE AND THE MEDIAL ACCESSORY OLIVARY NUCLEUS

Fig. 19–24

Figures 19–22 and 19–23. Tracts of the forebrain in a median and a right lateral view, respectively. Some of the nuclei are shown as stippled areas, and superficially situated tracts are also stippled. New tracts in stage 19 include the thalamostriatal tract (Stammbundel¨ of His or lateral prosencephalic fasciculus), around which the internal capsule continues to develop (but does not yet reach the pallium) (Fig. 19–24), the stria medullaris thalami, the fibers of the zona intrathalamica, and the amygdalo-habenular tract. The tract of the zona limitans intrathalamica later becomes the lamina medullaris externa. The sequence of appearance of the tracts is given in Appendix 4.

The fibers of the catecholamine neurons seem to penetrate no further than the ventricular eminences (Zecevic and Verney, 1995). At about this stage it has been found in the rat that septohippocampal projections reach the hippocampus, and that they are preceded by hippocamposeptal projections.

Lat. forebrain bundle

Med. ventricular eminence

Lat. ventricular eminence

Hypothalamic

sulcus

Figure 19–24. Beginning development of the internal capsule. Thalamostriatal fibers end abruptly in the medial ventricular eminence (cf. Fig. 5 in Richter, 1965), after having changed their direction at the ditelencephalic boundary (hemispheric stalk), where the fibers contribute to the lateral forebrain bundle (Stammbundel¨ of His, 1904). Corticothalamic fibers appear in stage 21 (Meyer et al., 2000). Their outgrowth (in the mouse) is influenced by Pax 6-positive cells at the corticostriatal boundary. Gene mutations (Pax 6 Sey/sey, Gbxc-2, f.ws.) cause defects of the internal capsule (Table 2 in Molnar´ and Butler, 2002). The level of this section is indicated in Figure 19–23.