Organization of the hypoglossal motoneurons that innervate the horizontal and oblique components of the genioglossus muscle in the rat.

Anatomical studies have shown the genioglossus muscle of the tongue of mammals to have at least two subdivisions. One is horizontal and the other fans out obliquely. In the dog, the hypoglossal nerve appears to have separate branches for each muscle subdivision. In the rat, genioglossus muscle motoneurons have been reported in the lateral and centrolateral subnuclei of the ventral hypoglossal nucleus. Here, retrograde labeling documented that these two hypoglossal sub-nuclei separately supply the two components of the genioglossus muscle. In so doing we add new data concerning the myotopic organization of the hypoglossal nucleus and further clarify the functional organization of the hypoglossal-tongue complex into protrusor and retrusor subdivisions.