The fine structure of cerebral blood vessels in chick embryo

The fine structure of the blood vessels was studied in the developing brain of chick embryo. The blood vessels were present in the embryos first examined (4 days after incubation) and their number increased in subsequent stages. The endothelial cells were generally large and showed junctional complexes, many microvilli and a large number of cytoplasmic organelles. Many tubular bodies and coated vesicles were also present. The tubular bodies were sometimes noted near the Golgi apparatus, suggesting their origin from this organelle. The mitochondria in the endothelial cells were generally larger than those in the surrounding neuropil. An ill-defined basement membrane-like substance was noted outside some endothelial cells on the 11th day and well formed basement membrane was present in the vessels of 18 day old embryos. A complete subpial astrocytic basement membrane was present from the early stage studied (4 days).