In some cases the aorta, instead of crossing to the left side of the spine, passes backwards towards its right side, and then either descends on the same side, or crosses over to the left behind the trachea and oesophagus.† In other cases there is a complete transposition of the viscera; and the direction of the heart and origins of its great vessels are altogether reversed, the systemic cavities of the heart being situated at the right side, and the pulmonic on the left, the aorta making its arch to the right side, and descending along the right side of the spine even to its termination in the iliac arteries. The vena cava in these cases descended on the left side of the spine, instead of on the right; the left carotid and left subclavian arose from an arteria innominata, on the right side of which arose separately from the arch the right carotid and right subclavian arteries.‡

* Treatise on the Blood, etc, p. 202. † Meckel, Anat., t. ii. p. 312.

‡ Phil. Trans. 1793; and Houston's Catalogue of Museum of Royal College of Surgeons, Ireland, p. 61.