[Development of the subclavian artery in the loggerhead turtle (Caretta caretta) studied by the injection method]

In the turtle, the left aorta and the pulmonary trunk originate from the right ventricle, while the right aorta takes its origin from the left ventricle as a functional systematic arch. The subclavian artery arises from the brachiocephalic artery on each side, and passes ventral to the vagus nerve and the jugular vein. These features are basically the same as in birds, and the subclavian artery of the adult turtle corresponds to a secondary artery from the viewpoint of comparative anatomy. Many investigators, including one of the present authors (Suzuki, 1987), have studied the development of the aortic arch and the subclavian artery in the chick embryo, but not in the turtle. The present authors examined it in Loggerhead turtle (Caretta caretta) embryos, from 14 days of incubation to completion of the aortic arch (27 days incubation). All blood vessels were injected with Berlin blue solution using a fine glass needle inserted into the aortic trunk through the ventricle of the heart. The following results were obtained. 1. In the turtle embryo the primary subclavian artery develops first, but is replaced by the secondary subclavian artery as in the chick. 2. The primary subclavian artery arises from the 12th dorsal intersegmental artery and passes dorsal to the posterior cardinal vein. In the 16-day embryo, it gives rise to capillary nets both cranially and caudally at the base of the forelimb bud along the inner surface of the thoracic wall. 3. At 19 days of incubation, a small blood vessel arises from the aortic sac at the origin of the third aortic arch and passes laterally, ventral to the anterior cardinal vein. The vessel then extends caudally, and finally, at 21 days of incubation, connects to the cranial part of the capillary net of the primary subclavian artery at about the middle of the lateral thoracic wall. After the completion of the connection, the vessel from the aortic sac is called by the name "the secondary subclavian artery." 4. The secondary subclavian artery gradually increases in size, while the proximal part of the primary one begins to atrophy and finally disappears at 27 days of incubation. After this, the forelimb bud receives its blood supply only from the newly-formed secondary subclavian artery. 5. In conclusion, in the turtle, the secondary subclavian artery is formed by connection of the primary artery with the caudally extending artery arising from the aortic sac, while in the chick it is derived from an outgrowth of the primary artery.(ABSTRACT TRUNCATED AT 400 WORDS)