MOTOR NUCLEI OF NERVES INNERVATING THE TONGUE AND HYPOGLOSSAL MUSCULATURE IN A CAECILIAN (AMPHIBIA, GYMNOPHIONA), AS REVEALED BY HRP TRANSPORT

The organization of the motor nuclei of the glossopharyngeal, vagal, o ccipital, first spinal and second spinal nerves of Typhlonectes natans (Amphibia: Gymnophiona: Caeciliaidae: Typhlonectinae) was studied by using horseradish peroxidase reaction staining. Each nucleus has discr ete patterns of cytoarchitecture and of topography. Nuclei are elongat e and some overlap anteroposteriorly. The brainstem is elongate, with no distinct demarcation of brainstem from spinal cord. The occipital n erve emerges through a separate foramen from that for the vagus and gl ossopharyngeal nerves in the species studied, is distinct from both, a nd its nucleus is more similar to spinal nuclei in cytoarchitecture. T he occipital nerve fuses with spinal nerves 1 and 2 to contribute to t he hypoglossal trunk. A spinal accessory nerve is absent. (C) 1996 Wil ey-Liss, Inc.