ORGANIZATION OF MOTONEURONS INNERVATING THE AXIAL MUSCULATURE OF THE BROWN CAIMAN (CAIMAN CROCODILUS FUSCUS)

The primary divisions of the spinal nerve in the brown caiman characte ristically show the following features: (1) the medial ramus was lies in the thoraco-lumbar and caudal regions, and (2) the first cervical a nd hypoglossal nerves form a single nerve complex from which the ventr al and dorsal rami extend. Intramuscular injections of horseradish per oxidase (HRP) established the positions of motoneurons whose axons fol lowed the primary rami. In the ventral horn of the thoracic and caudal spinal cord, the motoneurons of the medial ramus lie ventrally. These motoneurons lie between the epaxial and hypaxial motoneurons. At the spinomedullary junction, the pools of motoneurons innervating the infr ahyoid, lingual, and dorsal muscles have a somatotopic organization si milar to that observed in the thoraco-lumbar and caudal regions. Thus clear somatotopic organization of the motoneurons that innervate the a xial musculature exists at all spinal levels. (C) 1994 Wiley-Liss, Inc .