_L._ The venous trunks. 1, The caudal vein. 2, The coccygeo-mesenteric vein. 3, The posterior mesenteric vein. 4, The anterior mesenteric vein. 5, The gastro-duodenal vein. 6, The portal vein. 7, The hepatic vein. 8, The left anterior vena cava. 9, The left pectoral vein. 10, The left brachial vein. 11, The left jugular vein. 12, The right jugular vein. 13, The right brachial vein. 14, The right pectoral vein. 15, The right anterior vena cava. 16, The posterior vena cava. 17, The common iliac vein. 18, The femoral vein. 19, The renal vein. 20, The internal iliac vein. 21, The hypogastric vein. 22, The auricular portion of the heart. 23, The ventricular portion of same. ] The _pulmonary arterial trunk_ is given off from the conus arteriosus of the right ventricle. It is guarded at its origin by three semi-lunar valves similar to those of the aorta. The trunk divides into two pulmonary arteries, which are short, one called the pulmonalis dexter and the other the pulmonalis sinister. The former goes to the right and the latter to the left lung. Each branch penetrates the lung near the bronchus. These arteries divide, or branch, similarly to the bronchi. Following the branchings of the bronchi, they finally terminate into the lung capillaries, forming networks on the bronchi and the air-tube terminals. BRANCHES OF THE BRACHIO-CEPHALIC ARTERY ( Thyroidea ( ( Cervicalis inferior ( Vertebralis ( Vertebralis anterior ( ( Vertebralis posterior ( ( Arteria cervicalis ascendens ( Bronchiales ( Truncus ( Inferior esophageal ( caroticus ( Subcutaneous colli ( ( ( Carotis cerebralis ( ( Carotis ( Cervicalis superior ( ( communis ( Occipitalis ( ( ( Carotis externa ( ( Spinalis anterior ( Basilaris ( Cerebelli inferior Brachio-cephalic ( ( ( Clavicularis ( ( Sterno-clavicularis ( Sternalis ( ( ( Acromialis ( ( ( ( ( Subscapularis ( ( ( ( Ulnaris ( Subclavia ( Axillaris ( Brachialis ( Brachialis profunda ( ( ( Radialis ( ( Humeralis ( Circumflex humeralis ( ( ( anterior (