160 



Scientific Proceedings, Royal Dublin Society. 



right vertebral and the arteries of the right arm, arises from the descending 

 aorta dorsally and slightly caudal to the left subclavian : it passes dorsal to 

 the heart and oesophagus, and appears on the right side in its proper position 

 in the vicinity of the first rib (figure 2). The arrangement of the nerves is 



Fin. 2. — Abnormal Eight Suhclavian. 



normal ; the recurrent branch of the vagus returns round the ligamentum 

 arteriosum (the solidified ductus arteriosus) on the left, and on the right 

 takes its usual course round the position of the subclavian branch of the 

 innominate, even though the vessel which it would embrace normally is 

 absent. 



Abnormalities of a similar nature in the human subject have been 

 reported, and the phenomenon has been attributed to the persistence of 

 embryological conditions. 1 Mr. Kamsey Smith records the occurrence of a 

 similar abnormal right subclavian in a rabbit, 2 but he does not mention the 

 arrangement of the nerves associated with it. 



The origin of the aortic arches in the mammalian blood system is 



1 Quain's " Anatomy," 9fch edition, vol. i. Macalister s "Human Anatomy," \i 

 pp. 555, 556, 



2 " Journal of Anatomy and Physiology," April, 1891. 



