Ontogenic development of the human subcommissural organ

The structure of the human sub commissural organ during its ontogenic development in 24human embryos and foetuses ranging from 6 to40 weeks of gestation (WG), and three adult human brains from 27-, 65- and 70-year old subjects was investigated using both qualitative and quantitative methods. Concurrently, the appearance of the sub commissural organ, pineal gland and mesocoelic recess was determined by studying their structure, length and volume. The human SCO appears at the beginning of 8th WG, which confirms previous results; the complete maturation of the SCO occurs at the 15th WG and the following three parts can be distinguished: the precommissural part, located in the rostral zone of the posterior commissure (PC) and extending to the pineal recess; the subcommissural part, located under the PC, and the retro commissural part, located in the caudal zone of the PC, in the mesocoelic recess and at the beginning of the Sylvian aqueduct. The reduction in size of the SCO begins after the 17th WGand this decrease in size begins in the precommissural, continues in the subcommissural, and finishes in the retro commissural part. The regression and atrophies of the SCO begin after birth, and the SCO disappears completely after the age of 30. The mesocoelic recess starts to form at the beginning of the 10th WG, and is completely formed by the 14th WG and this is where the retrocommissural part of the SCO is located. In the40th WG the regression of the mesocoelic recess begins and this takes place at the same time as the regression of the SCO. A parallel development between the SCO and the pineal was found. Thus, we observed the first appearance of the pineal recess in the 7-8th WG; during the 10thWG a compact mass of cells appeared in the rostral part of pineal recess and by the 15th WG the pineal gland (PG) had acquired an almost definitive aspec