Presence of a pineal nerve (nervus pinealis) in the human fetus: a light and electron microscopical study of the innervation of the pineal gland.

The presence of a hitherto undiscovered nerve located in the subarachnoidal space just caudal to the pineal organ, connecting this organ and the posterior commissure, was demonstrated by light and electron microscopy in a series of 18 human fetuses. This nerve is believed to be ontogenetically equivalent to the pineal nerve observed in the anuran amphibians. The nerve was present in fetuses with a CRL of 56 mm and had not disappeared in fetuses with a CRL of 169 mm. The gestational age at which this human fetal nerve degenerates could not be determined in this study. In addition to the bilateral conarian nerve a habenulopineal tract and an intrapineal ganglion were observed. The presence of the classical Pastori and Marburg ganglia was confirmed, and a new ganglion lying rostral to the pineal organ was seen too.