Passage of Harderian gland secretions to the vomeronasal organ of Thamnophis sirtalis (Serpentes : Colubridae)

The Harderian gland is a poorly understood structure found in the anterior orbit of most terrestrial vertebrates. In colubrid snakes it is a seromucou s gland with a large postorbital portion. Numerous functions have been ascr ibed to this gland, including contributions to orbital lubrication or the v omeronasal system. Anatomically the Harderian gland is connected to the vom eronasal organ (VNO) via the nasolacrimal duct. In this study we traced the serous secretions of the Harderian gland of two subspecies of Thamnophis s irtalis (Colubridae), using autoradiographic techniques at the light-micros copic level. We injected the Harderian gland of the snakes with H-3-proline either unilater ally (right side) or bilaterally. The right Harderian glan ds of both treatment groups were then injected with a potassium-rich soluti on. No labeling was observed in the orbital space of any treatment group, s uggesting that the Harderian gland secretions of T. sirtalis do not functio n in orbital lubrication. Labeling was only observed in the right Harderian gland, Harderian gland ducts, nasolacrimal duct, apical vomeronasal sensor y epithelium, VNO lumen, and vomeronasal duct. No such labeling was observe d in any of the other treatments examined. Thus, the serous secretions of t he Harderian gland in snakes flow to the VNO, and may be considered part of the vomeronasal system. The specific function of the Harderian gland secre tions in the vomeronasal system remains to be determined.