The Proper Phrenic Arteries, called also the inferior phrenic or sub-phrenic, are the first branches of the abdominal aorta; they arise immediately above the cceliac axis, from the front of the vessel. The artery on the right side passes upward, forward, and outward, between the right crus of the diaphragm, which lies behind it, and the inferior cava, which is in front: that of the left side takes a similar direction, separating the left crus of the diaphragm from the oesophagus. Having arrived at the posterior extremity of the cordiform tendon of the diaphragm, each artery communicates behind this tendon with its fellow of the opposite side, and then divides into external and anterior branches; these ramify in the substance of the diaphragm, and inosculate with the other arteries which supply this muscle. The artery of the right side sends branches to the liver through its coronary ligament, and that of the left side sends a branch to the oesophagus. The external branches anastomose with the intercostal arteries; and the anterior branches communicate with the internal mammary, and with the branches of the opposite side, in front of the cordiform tendon: in this manner there is a kind of arterial circle formed around this tendon.

Soon after its origin, the inferior phrenic gives off the superior capsular artery, to supply the upper portion of the suprarenal capsule.

The Middle Capsular Arteries

The Middle Capsular Arteries are usually two in number, viz. one on each side: they arise from the aorta a little above the renal. Each of them proceeds transversely outwards, to arrive at the concave margin of the corresponding supra-renal capsule, and divides into a number of branches which ramify in the sinuosities on its anterior and posterior surfaces, and in its interior. In this course it gives a few branches to the pillars of the diaphragm, to the psoas muscle, and to the adipose and areolar tissue in the neighborhood.