The episternal or interclavicular region is a locality traversed by so many vitally important structures gathered together in a very limited space, that all operations which concern this region require more steady caution and anatomical knowledge than most surgeons are bold enough to test their possession of. The reader will (on comparing Plates 9 and 10) be enabled to take account of those structures which it is necessary to divide in the operation required for ligaturing the innominate artery, A, Plate 9, or either of those main arterial vessels (the right common carotid and subclavian) which spring from it; and he will also observe that, although the same number and kind of structures overlie the carotid and subclavian vessels, A B, of the left side, Plate 10, still, that these vessels themselves, in consequence of their separate condition, will materially influence the like operation in respect to them. An aneurism occurring in the first part of the course of the right subclavian artery, at the locality a, Plate 9, will lie so close to the origin of the right common carotid as to require a ligature to be passed around the innominate common trunk, thus cutting off the flow of blood from both vessels; whereas an aneurism implicating either the left common carotid at the point A, or the left subclavian artery at the point B, does not, of course, require that both vessels should be included in the same ligature. There seems to be, therefore, a greater probability of effectually treating an aneurism of the left brachio-cephalic vessels by ligature than attaches to those of the right side; for if space between collateral branches, and also a lesser caliber of arterial trunk, be advantages, allowing the ligature to hold more firmly, then the vessels of the left side of the root of the neck manifest these advantages more frequently than those of the right, which spring from a common trunk. Whenever, therefore, the "peculiarity" of a separate aortic origin of the right carotid and subclavian arteries occurs, it is to be regarded more as a happy advantage than otherwise. DESCRIPTION OF PLATES 9 & 10. PLATE 9. A. Innominate artery, at its point of bifurcation. B. Right internal jugular vein, joining the subclavian vein. C. Sternal end of the right clavicle. D. Trachea. E. Right sterno-thyroid muscle, cut. F. Right sterno-hyoid muscle, cut. G. Right sterno-mastoid muscle, cut. a. Right vagus nerve, crossing the subclavian artery. b. Anterior jugular vein, piercing the cervical fascia to join the subclavian vein. [Illustration: Neck and upper chest, showing blood vessels, muscles and other internal organs.] Plate 9 PLATE 10. A. Common carotid artery of left side. B. Left subclavian artery, having b, the vagus nerve, between it and A. C. Lower end of left internal jugular vein, joining-- D. Left subclavian vein, which lies anterior to d, the scalenus anticus muscle.