5. =Sinus columnæ vertebralis.=--On the ventral surface of the vertebral canal, beneath the periosteum, are two wide venous sinuses, one on each side of the middle line. These sinuses extend the entire length of the spinal cord. At the atlantal foramen each sends a strong branch to the internal jugular vein. Farther caudad they send branches to the vertebral, intercostal, and lumbar veins, and communicate with each other by numerous transverse branches. They receive many small veins from the spinal cord. 3. =Vena cava inferior= (Fig. 129, _c_; Fig. 126, _a_). The inferior vena cava (Fig. 126, _a_) is formed at about the level of the last lumbar vertebra by the union of the two =common iliac= veins (Fig. 126, _w_). It passes craniad near the dorsal median line, lying at first dorsad of the aorta (_b_), then to the right, then ventrad. It enters the substance of the liver in the dorsal part of the caudate lobe of the latter, passes through the liver, and then through the diaphragm near the ventrolateral edge of the central tendon. It passes then craniad in the thoracic cavity (Fig. 129, _c_) ventrad of the caudal lobe of the right lung, and enters the right auricle. It receives the following branches (Fig. 126): =lumbar=, =iliolumbalis= (_v_), =spermatica interna= (_u_), =renal= (_t_), =adrenolumbalis= (_s_), =phrenic=, and =hepatic= veins. All but the last two named accompany the arteries of the same name. =V. phrenica.=--The phrenic veins gather the blood from the diaphragm and empty into the vena cava as it penetrates the diaphragm. =V. hepatica.=--The hepatic veins vary in number. They gather the blood from the liver (sent in by the portal vein and hepatic arteries) and enter the vena cava just caudad of the diaphragm. VENA PORTÆ. THE PORTAL VEIN (Fig. 131).--The =portal= vein is the large vein carrying the blood from the abdominal viscera to the liver. Within the liver the portal vein breaks up into capillaries; these collect to form the =hepatic= veins, which enter the vena cava inferior. The portal vein (_a_) is formed near the pyloric end of the stomach (1) by the union of the =superior mesenteric= (_b_) and =gastrosplenic= (_c_) veins and passes thence along the ventral border of the foramen epiploicum (foramen of Winslow) to the liver (2), where it divides, going to the lobes of the liver. On its way to the liver it may receive the =pancreaticoduodenalis= (_d_), =gastroepiploica= (_e_), and =coronaria ventriculi= (_f_). These may unite with the portal separately, or any two or all three may unite to form a single trunk before entering the portal vein. 1. =V. coronaria ventriculi= (_f_) gathers the blood from the lesser curvature of the stomach and anastomoses with the gastrosplenic veins. It usually empties into the portal vein near the pylorus. 2. =V. pancreaticoduodenalis= (_d_) receives the blood from the pancreas and first part of the duodenum, and empties into the vena portæ near to or with the preceding.