Morphology of the Harderian gland of the snakes Spalerosophis diadema and Psammophis sibilans

The current study aims to demonstrate the morphological differences in the Harderian gland between two species and to explore whether these differences are related to their activity patterns or not: Spalerosophis diadema, which exhibits both nocturnal and diurnal activity, and Psammophis sibilans, which is mainly diurnal. Anatomical investigation has been found a sole orbital gland in S. diadema and P. sibilans which is the Harderian one. It is voluminous, whitish in color, well developed, and multilobular structure. It has been divided into four distinct portions: the body, anterior lobe, ocular, and postorbital one. The Harderian gland lies on the innerventral surface of the orbit, and its surface featured pores and projections. The body of HG of S. diadema contains more pores and projections than that of P. sibilans. The anterior lobe of the HG in S. diadema and P. sibilans extends forward beneath the prefrontal bone. The ocular and postorbital lobes in S. diadema and P. sibilans extend posterior to the eyeball. The postorbital lobe of S. diadema is readily visible when the skin has been removed. The postorbital lobe of P. sibilans has been hidden by levator anguli oris muscle. Histologically, lobes of HG in these two snake species exhibit a homogeneous structure, characterized as a compound tubuloacinar type. The acini of this gland were lined by long columnar glandular cells in a single row surrounding a lumen. Histochemical analysis of the HG of the S. diadema and P. sibilans showed that the glandular cells give a positive reaction with PAS and a positive reaction with mercury-bromophenol blue while weakly reaction to Alcian Blue at pH 2.5. Although the HG of S. diadema and P. sibilans share the same structure, there is notable interspecific variation in their size, Poreferation, and surface projections. In the two sympatric species, the size of the HG may be due to their respective activity patterns; the species that is both nocturnal and diurnal tends to have larger HGs than the strictly diurnal one. Additionally, the postorbital lobe of the HG in P. sibilans is obscured by the levator anguli oris muscle that position facilitates the release of the secretion.