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Microvascularization of the brain cortex was investigated in 21 brains of human fetuses, from 15th to 25th postovulatory week and one adult human brain. Blood vessels injected with ink-gelatine solution were examined on preparations lighted by the Spalteholz method. In all examined stages of fetal development as well as in the adult brain a regular geometric arrangement of the blood vessels which radially penetrated the brain substance was observed. Centrally placed vascular trunk of bigger diameter surrounded by the blood vessels of smaller calibre was registered. On the basis of the obtained results it can be concluded that the vascularization of the brain cortex in all examined stages of the development follows the pattern of radially placed vascular units.

A study of the volume density of the ganglionic eminence vascular network and the constituent parts of the corpus striatum was performed on 8 chosen foetal brains, which were well-injected with a mixture of India ink and gelatin, aged from 14-25 postovulatory weeks. The volume density of the ganglionic eminence vascular network amounts to 0.0209-0.0300 mm0, of the caudate nucleus to 0.0131-0.0181 mm0, of the putamen to 0.0136-0.0159 mm0, and of the globus pallidus to 0.0121-0.0159 mm0. The comparison of the results obtained, shows that the volume density of the ganglionic eminence vascular network is higher than the volume density of the other examined structures and that this difference is statistically highly significant (p less than 0.01). The augmented volume density of the ganglionic eminence vascular network points to a possibility of slow blood flow through its vascular bed, which was experimentally demonstrated on animals. This slow blood flow, among other factors, may be the cause of a ganglionic eminence venous infarction in premature newborns of low birthweight.

The blood vessels of the insular cortex and the claustrum were studied in 26 foetal brains of 16--25-week-old foetuses and one adult brain without noticeable pathological signs. The labelling of the vessels was wade according to Duvernoy et al. (1981). In 16-week-old foetuses arteries of types A6 as the A5 were found in the insular cortex as well as the veins of type V5. In 19-week-old foetuses the arteries of type A4 and the veins of type V4 appeared as only cortical vessels. In the following stages of the brain development the shorter and shorter arteries appeared so that in 24-week-old foetuses one could see all the types of arteries from A6 to A1. However, in the period from 19 to 25 weeks, no vein shorter than that of the type V4 was found in the insular cortex. In the adult brain it was possible to identify all the types of arteries and veins in the insular cortex, but distances between the individual vessels were larger in comparison with those in the insular cortex of the foetal brains. There claustrum was vascularized by the arterial branches from the insular arteries, whereas in the adult brain the claustrum received some of the branches from the striate arteries as well. This pattern of the vascular supply may indicate the common origin of the claustrum and the insular cortex.

The development of the blood network of the dentate nucleus was studied on 20 human fetal brains of different crown-rump length (CRL). In the stage of 17 to 20 weeks, the blood network of the dentate nucleus consisted of moderate spiral blood vessels. They anastomosed each other and made irregular elongated polyhedral meshes. From this meshwork, blood vessels of a greater volume arose and extended to the hilum of the nucleus. Between 23 and 25 weeks, a clear segmental vascular pattern was noticed. The capillary network was very dense. Along the outer surface of the nucleus the blood vessels which connected two secondary wrinkles of the gray matter were observed. In all the stages investigated the blood vessels were moderately spiral.