A. subclavia dextra as the last branch of the Arcus aorticus in Sus scrofa domestica

Abstract

After having dissectcd more than one hundred swine specimens, aiming to find out the behaviour of the collaterals of the A. bruchioccphalica, we had the opportunity to record a case of an A. subclavia dextra as the last branch of the aortic arch. Such finding was shown up in one male fetus near term, measuring 24.5 cm, proceeding from Frigorífico Armour of São Paulo, and the only one among the group belonging to the same uterus which revealed the following special points: the first large branch to leave the aortic arch, at 10 mm from its origin, was the Trnncus bicarol, icus, which divided into the A a. carótides communes sinistra and dcxlra. Distally to the above mentioned trunk and at intervals of 1.9 mm, the emergence of the Aa. subclaviae sinistra and dextra has been observed. The first three branches showed normal origin and course, in opposition to the happening of the last one, which coining forth in the terminal part of the aortic arch at once passed the median line by crossing dorsally the esophagus and trachea, between these formations and the tract of the column corresponding to the articulation of the 3th and 4th thoracic vertebrae. Both esophagus and artery did not present cither signs of compression or decrease of caliber. All the collaterals of the right subclavian artery showed normal disposition, which was also seen relatively to the Ansa subclavia. In respect to the right N. laryngcus caudalis. we have not seen the common disposition; indeed, it detached from the N. vagus opposite the joint between the 5th and 6th cervical vertebrae, therefore without winding around the homolateral subclavian artery. We are offering an embriologie interpretation of the anomaly which we believe to be very rare, according to the scarce references in the literature dealing with the variations of the aortic arch in domestic animals.