The anterior mesenteric artery of two species of fowl, the turkey and chicken, is found to differ structurally from the basic pattern observed in other avian arteries and in mammalian arteries in general. This difference in structure lies in the fact that the avian anterior mesenteric artery contains two well-developed muscular components: an inner circular, and an outer longitudinal, analogous to the arrangement of the muscularis externa of the intestinal wall. However, the evidence presented indicates that the outer longitudinal layer is part of the adventitia. The possible functional significance of this feature is discussed.In recent years studies on the vasculature of birds have dealt primarily with the aorta and coronary arteries, particularly with reference to atherosclerosis. In this laboratory, interest in the problem of dissecting aneurysm of the aorta of turkeys led to the examination of other arteries. During this examination, the anterior mesenteric artery, which originates from the aorta immediately posterior to the point of origin of the coeliac artery, was noted to have a unique structure unlike that of other arteries of the bird.
MATERIALS AND METHODSIn this study, 66 turkeys ranging from three to 30 weeks of age, mostly males, and five adult White Leghorn hens were dissected. In one freshly-killed bird, the viscera were reflected with minimum disturbance of the vasculature, and the aorta was clamped with a hemostat immediately distal to the origin of the right brachiocephalic artery. Melted agar, containing basic fuchsin dye, was then injected into the aorta, distal to the clamp. When the bird was cooled, the dye-agar mixture permitted better visualization of the smaller visceral arteries.In four birds, the following arteries were examined histologically : anterior mesenteric, coeliac, sciatic, carotid, and iliac. Other arteries and branches of the above were examined randomly from several other birds, and in at least two birds, a detailed examination was made of the proventricular, gastric, hepatic, splenic, pancreato-duodenal, and renal arteries, and of the distal branches of the anterior mesenteric artery.Vessels were fixed in 10% formalin or in formalin-sublimate-acetate fixative and stained by hematoxylin and eosin or by use of an improved technique for demonstrating all connective tissue elements in a single section devised by Movat ('55). Movat's technique proved so highly satisfactory for differentiating elastic tissue, collagenous fibers, and smooth muscle elements, that it was routinely employed for this purpose. Briefly, this technique is as follows:Tissues are fixed for 12 to 18 hours in formalin-sublimate-acetate (80 ml of disstilled water, 4 gm of mercuric chloride, 20 ml of 36-40% formaldehyde solution, and 5 ml of acetic acid). Dehydration, clearing, and embedding were handled in the usual manner. The stains used are a combination of Weigert's iron-hematoxylin for nuclei, woodstain scarlet-acid fuchsin for cytoplasm, resorcin-fuchsin for elastic tissue, saffron for collag...
