A macroscopic study of the internal thoracic artery of the rat.

The internal thoracic artery (ATI) of rats was macroscopically studied. In this study, the overall features of the artery were virtually elucidated in entirety. The artery was found to arise from the subclavian artery in the thoracic cavity and to immediately break up into the following branches: (1) the pericardiacophrenic artery, (2) the superior epigastric artery, (3) the thymic branch, (4) the comitans branch to the brachiocephalic veins, and finally (5) the bronchoesophageal trunk. As is well known, rats are devoid of the superior caval veins, retaining instead a pair of brachiocephalic veins into adulthood; this is a greatly beneficial condition as it enables us to consider the essential relationships of the ATI to relevant structures which are thought to be directly involved in the development of the ATI. In fact, the rat ATI revealed topographically a remarkable intimacy with the phrenic nerve, the brachiocephalic and inferior caval veins, the heart and lungs and also with the diaphragm; in their development all are in close relationship with the pleuropericardial fold. This fact leads us to the opinion that, for a better understanding of the morphological meanings of the ATI, an understanding of the relationship of this artery to the pleuropericardial fold seems to be a prerequisite.