Topography and Microscopic Anatomy of the Testes of the Swan

Abstract

In birds, unlike most mammals, the testes remain in the same position in the abdomen throughout life. In the adult swan the paired organs are located caudal to the lungs (Fig. 1), separated by parts of the diagonal and horizontal septum; they are situated in the cranial area of the cavitas peritonealis intestinalis. The testes are each attached medially to the back abdominal wall by a short mesorchium. They lie on either side of the dorsal mesenterium, slightly displaced in a lateral direction, ventrally to the caudal end of the adrenal glands and the cranial pole of the heavily lobed kidneys. The testes are further separated from these two retroperitoneal-lying organs by the walls of the abdominal air sacs. These walls, also covered by peritoneal epithelium, are fused dorsally with the peritoneal lining of the back abdominal wall to a far extent laterally. Medially in the region caudal to the testes, this fusion reaches the dorsal mesenterium, but in the area of the testes themselves it only reaches to about the middle of each adrenal gland. Therefore in the swan the testes do not bulge into the abdominal air sacs as they do in other birds (Duncker 1979), but are located on each side in a pocket made from the dorsal mesenterium and the dorsomedial wall of the air sac. This position has only previously been described for the left ovary in the domestic hen (McLelland and King 1970). The wall of the air sac rests displaceably on the surface of the testicle and is unusually delicate in spite of its three layers of air sac epithelium, connective tissue, and peritoneum. However, the assumption of Cowles and Nordstrom (1946) that the abdominal air sacs play a role analogous to that of the scrotum of mammals in cooling the testicle is false.