Isthmus Cerebri

ISTHMUS CEREBRI, cerebral isthmus, corresponds to the upper part of the pons Varolii, which narrows at this point, as does the fourth ventricle, which transitions into aqueduct of Sylvii; the lateral walls of the pons here become free, not connected with the cerebellum. In the isthmus cerebri are located the brachia conjunctiva and velum medullare anterius, through which pass fibers of the Gowers bundle and roots of the trochlear nerve, lemnisci, which at this level reach the surface in the form of a triangular field (trigonum lemnisci). The isthmus cerebri belongs to the fourth division of the brain, developing from the posterior cerebral vesicle. Functions and pathology correspond to the structures passing through here.