ORIGINAL ARTICLE Histomorphology of the Harderian Gland in the Angora Rabbit A. G. Bayraktarog ˘ lu 1 * and E. Ergu ¨n 2 Addresses of authors: 1 Department of Histology and Embryology, Faculty of Veterinary Medicine, University of Ankara, 06110 Diskapi, Ankara, Turkey; 2 Department of Histology and Embryology, Faculty of Veterinary Medicine, Kirikkale University, 71451 Yahsihan, Kirikkale, Turkey Introduction The Harderian gland (Glandula profunda palpebrae terti- ae) is an exocrine gland with a secretion of varying char- acter in mammals, birds, rodents, amphibians and reptiles. Amongst mammalian species, the Harderian gland is reported to be absent in bats and terrestrial car- nivores and is known to be rudimentary in monkeys (Baccari et al., 1996). Three distinct types of the gland, which vary by the morphology of the epithelial cells and the lobulation pattern, have been reported in avian spe- cies (Burns, 1992). In reptiles, the gland is composed of three lobes, namely the medial, intermediate and lateral lobes (Baccari et al., 1990). In rabbits, the Harderian gland is an intra-orbitally located tubuloalveolar gland composed of two distinct parts, viz. a pink lobe and a white lobe (Eglitis, 1964; Payne, 1994; Janssens et al., 1999). Based on the variety of its secretory products, the Harderian gland has numerous functions, including the *Correspondence: Tel.: +90 312 3170315; fax: +90 312 316 44 72; e-mail: dralevgurol@gmail.com With 10 figures Received May 2009; accepted for publication June 2010 doi: 10.1111/j.1439-0264.2010.01020.x Summary This study was aimed to demonstrate the morphological and histochemical properties of the Harderian gland in the Angora rabbit. Ten healthy adult Angora rabbits obtained from private breeders constituted the material of the study. The Harderian gland, which is composed of the pink and white lobes, consists of cells that produce a secretion of lipid character. The pink lobe con- tained type I cells with large lipid vacuoles. Cells with small lipid vacuoles (type II) were found in the white lobe. Type III cells containing both large and small lipid vacuoles were not observed. While type I cells reacted strongly to staining with Oil red O, type II cells reacted weakly to this stain. The number of plasma cells was greater in the white lobe when compared to the pink lobe. The apical granules within the epithelial cells lining the intralobular and inter-lobular excretory ducts of the gland were positive for periodic acid-Schiff (PAS), peri- odic acid-Schiff/alcian blue (PAS/AB), alcian blue (AB) and performic acid/ alcian blue (PA/AB). Electron microscopic examination revealed that type I cells contain large electron-light lipid vacuoles and an eccentric heterochro- matic nucleus, due to the presence of these vacuoles. The cells, which were connected by tight junctions, possessed apically located microfolds. The nucleus of type II cells was situated basally and had an oval shape. Type II cells had apical microvilli-like cytoplasmic protrusions, longer than those of type I cells. Oval shaped myoepithelial cells were observed between the glandular epithelial cells and their basal lamina. The epithelium lining the excretory ducts of the gland contained two types of granules, which were dark and lightly coloured. Histochemical and ultrastructural examinations revealed no difference in the structure of the Harderian gland between female and male Angora rabbits. Anatomia Histologia Embryologia 494 ª 2010 Blackwell Verlag GmbH • Anat. Histol. Embryol. 39 (2010) 494–502