posterior commissure in dogs

Rounded band of white fibers crossing the middle line on the dorsal aspect of the upper end of the cerebral aqueduct. It is important in the bilateral pupillary light reflex. Its fibers acquire their medullary sheaths early, but their connections have not been definitely determined. Most of them have their origin in a nucleus, the nucleus of the posterior commissure (nucleus of Darkschewitsch), which lies in the central gray substance of the upper end of the cerebral aqueduct, in front of the nucleus of the oculomotor nerve. Some are probably derived from the posterior part of the thalamus and from the superior colliculus, whereas others are believed to be continued downward into the medial longitudinal fasciculus. The posterior commissure interconnects the pretectal nuclei, mediating the consensual pupillary light reflex[WP]. Diencephalic tract which is located in the vicinity of the dorsal diencephalon and mesencephalon and connects the pretectal nuclei. From Neuroanatomy of the Zebrafish Brain[ZFA]. Every claim on this page comes from the Leumas anatomy graph and carries its source.

What the posterior commissure is

Rounded band of white fibers crossing the middle line on the dorsal aspect of the upper end of the cerebral aqueduct. It is important in the bilateral pupillary light reflex. Its fibers acquire their medullary sheaths early, but their connections have not been definitely determined. Most of them have their origin in a nucleus, the nucleus of the posterior commissure (nucleus of Darkschewitsch), which lies in the central gray substance of the upper end of the cerebral aqueduct, in front of the nucleus of the oculomotor nerve. Some are probably derived from the posterior part of the thalamus and from the superior colliculus, whereas others are believed to be continued downward into the medial longitudinal fasciculus. The posterior commissure interconnects the pretectal nuclei, mediating the consensual pupillary light reflex[WP]. Diencephalic tract which is located in the vicinity of the dorsal diencephalon and mesencephalon and connects the pretectal nuclei. From Neuroanatomy of the Zebrafish Brain[ZFA]. The atlas records it as a nerve at the organ scale in the dog.

Where the posterior commissure is

It sits within the nervous system. Not positioned individually. Drawn inside the structure this dataset says contains it — the containment is asserted, the exact spot within it is not.

What the posterior commissure connects to

The atlas records 7 typed relationships for it, across 3 kinds of connection. part of brain, diencephalic white matter and diencephalon, and 1 more.

Supply and innervation

This dataset asserts no arterial supply, venous drainage or innervation for the posterior commissure. Only a minority of structures carry those edges here, so an empty answer means nothing has been recorded — not that there is nothing to record.

Also called

Also recorded as caudal commissure, epithalamic commissure, commissura epithalami, commissura epithalamica, commissura posterior and posterior commissure (Lieutaud). Searching any of those names reaches this page.

Source

Uberon multi-species anatomy ontology (Mungall et al.), CC BY 4.0. Term UBERON:0000936, version 2026-06-19, retrieved 2026-08-24. Licence: CC-BY-4.0.

Questions

Where is the posterior commissure?

It sits within the nervous system. Not positioned individually. Drawn inside the structure this dataset says contains it — the containment is asserted, the exact spot within it is not.

What does the posterior commissure connect to?

Part of: brain, diencephalic white matter, diencephalon and white matter.

Is the posterior commissure the same in other species?

This page describes the dog. The human record of the same structure sits beside it on /compare, over one shared model rather than two atlases built separately.