The diaphragm is pierced by three foramina. (1) The =hiatus aorticus= is an interval between the two crura and below the last thoracic vertebra. It contains the posterior aorta, vena azygos, and cisterna chyli. (2) The =hiatus œsophageus= (or foramen sinistrum) perforates the right crus near its junction with the tendinous center. It is situated a little to the left of the median plane and two or three inches below the thirteenth thoracic vertebra (in expiration). It transmits the œsophagus, the vagus nerves, and the œsophageal branch of the gastric artery. (3) The =foramen venæ cavæ= (s. dextrum) pierces the tendinous center about an inch to the right of the median plane, and about six inches below the twelfth thoracic vertebra (in expiration). The vena cava is firmly attached to the margin of the opening.[49] _Relations._—The thoracic surface is related to the endothoracic fascia, pleuræ, pericardium, the bases of the lungs, and the ribs in part. The abdominal surface is in great part covered by the peritoneum, and is related chiefly to the liver, stomach, spleen, pancreas, kidneys and adrenals, and the anterior flexures of the colon. The sympathetic and splanchnic nerves pass between the crus and the psoas muscles on each side. The asternal vessels perforate the edge of the muscle at the ninth costo-chondral joint. _Blood-supply._—Phrenic and asternal arteries. _Nerve-supply._—Phrenic nerves (from the fifth, sixth, and seventh cervical nerves). THE ABDOMINAL MUSCLES The =superficial fascia= covering the lateral and ventral walls of the abdomen is continuous dorsally with the lumbo-dorsal fascia, in front with the thoracic fascia, and behind with the gluteal fascia. In the inguinal region it forms part of the fascia of the penis or of the mammary glands. At the lower part of the flank it forms a fold which is continuous with the fascia of the thigh near the stifle joint. In this fold are the precrural lymph glands. Medially it blends with the linea alba. It contains the abdominal portion of the panniculus carnosus.