Developmental history of nervus terminalis in embryos of insectivorous bats.

Insectivorous bat embryos (Tadarida and Myotis) ranging from 6- to 16-mm C-R length were examined for the presence of the nervus terminalis. These embryos have no vomeronasal nerve with which the nervus terminalis could be confused. The nerve and associated ganglion cells first appear in the 7-mm embryo. As the embryo ages, a gradual increase in nerve size and ganglion cell numbers occurs. In the 13-mm embryo, nerve size and ganglion cell numbers are reduced, and in older embryos both nerve and cells are absent, as in the adult. The ganglion cells arise as clusters from the nasal septal epithelium. The largest number of cell clusters occurs in the 10.5-mm embryo. Their number then decreases and none are present in embryos of 13-mm and longer. These cells migrate centrally along the course of the nerve which accompanies the olfactory nerve from the nasal cavity roof to a level just caudal to the olfactory bulb, where the nervus terminalis turns dorsalward along the medial telencephalic wall surface. Except in the youngest and oldest embryos the nervus terminalis, where present, divides into two or three branches to pierce the hemispheric wall, one usually entering the region of the nucleus olfactorious anterior, and the other(s), the region of the medial septal nucleus. In some cases, several ganglion cells are present along the intrahemispheric course of the nerve fibers. All ganglion cells resemble those in various sensory ganglia, and so, are probably also sensory neurons.