Can an orbital gland function in the vomeronasal sense? A study of the pygopodid Harderian gland

The Harderian gland occurs in the orbit of most tetrapod vertebrates. A growing body of evidence suggests that this gland is associated with the chemoreceptive function of the vomeronasal organ. In the present study, the morphology of the Harderian gland in two species of pygopodids was examined, and the results were contrasted with those from both geckos and snakes. The results show that the pygopodid Harderian gland shares histochemical and ultrastructural features with that of the geckos. However, in several gross morphological features, the pygopodid Harderian gland more closely resemble that of snakes than that of geckos. In both pygopodids and snakes, the nasolacrimal duct forms a direct link between the Harderian gland and the vomeronasal organ, which indicates that this specialized connection between the Harderian gland and vomeronasal organ is a convergent evolutionary attribute of these two groups.