Two cases of A. subclavia dextra as the last branch of the Arcus aorticus in the dog

Abstract

This note gives the description of two cases of right subclavian artery (A. subclavia dextra) as the last branch of the aortic arch, in the dog, found occasionally when the A. was studying the frequency of the Truncus bicaroticus. The abnormal right subclavian artery arises cranio-distally to the left subclavian artery (A. subclavia sinistra), running towards the thoracic limb, above the oesophagus. Among its collateral branches is noted the following alteration: the transverse artery of the neck (A. transversa colli), instead of emerging as usually by a common trunk with the deep cervical artery (A. cervicalis profunda) and supreme intercostal artery (A. intercostalis suprema), arises from the right subclavian artery isolated and proximally to the common stem of these two vessels. Besides these particular dispositions, both animals present the common carotid arteries (Aa. carotides communes) arising by a common long trunk (Truncus bicaroticus) and the right recurrent nerve (N. laryngeus candalis) as a cervical branch of the vagus nerve (N. vagus), i. e., without winding around either the right subclavian artery or the brachiocephalic artery (A. brachiocephalica) and therefore showing its recurrencial traject shorter than commonly. The oesophagus is not constricted at the arterial crossing place. While human anatomical literature points out hundreds of cases of right, subclavian artery as the last branch of the aortic arch, the comparative anatomical bibliography records the anomaly only in the hedgehog and in the rabbit (MECKEL, SMITH, EALES) as very rare findings. Attention is called to the virtual lack of sistematic researchs about the aortic collateral branches in comparative anatomy; the scanty and scattered cases referring to anomalies of the aortic collateral branches, in the dog, are summed up. In all these cases the greatest interest was ascribed to the constriction of the oesophagus; thus can be explained the omission of important anatomical details. The anomalies are described in two mongrel females: one is adult and the other a foetus at birth time. Both, the presence of the Truncus bicaroticus and the arising, course and relations of the right subclavian artery, besides the behaviour of the right recurrent nerve, permit a single description of the two cases. In the second one (foetus), however, it is worthy to note an unusual anastomotic branch that connects the left recurrent and right vagus nerves. Explanations of the vascular and nervous anomalies, under the embryological standpoint, are given; the possibility of demonstrating the hereditary nature of anomalies and variations of the aortic collateral branches in dogs, in the light of GIACOMINI (human), MILKS and WILLIAMS (dog), EDMONDS and SAWIN (rabbit) findings, is considered admissible. Anyway, according to DE GARIS, it is asserted that the Arcusaorticus corresponds to the most fitting anatomical structure for variation, symmetry and heredity studies.