958 THE VASCULAR SYSTEM. 



(3) The arcuate artery arises opposite the first cuneiform bone. It runs laterally, 

 on the bases of the metatarsal bones, deep to the long and short extensor tendons, supplies 

 the extensor hallucis brevis and the extensor digitorum brevis, and anastomoses with 

 branches of the lateral tarsal and lateral plantar arteries. It gives off three dorsal 

 metatarsal arteries, second, third, and fourth, which run forwards on the muscles which 

 occupy the three lateral interosseous spaces to the clefts of the toes, where each divides 

 into two dorsal digital branches for the adjacent sides of the toes bounding the cleft to 

 which it goes. The lateral side of the little toe receives a branch from the most lateral 

 dorsal metatarsal artery. Each dorsal metatarsal artery gives off a posterior perforating 

 branch, which passes through the posterior part of the intermetatarsal space, between 

 the heads of the dorsal interosseous muscle, to anastomose with the plantar arch, and 

 an anterior perforating branch, which passes through the anterior part of the space 

 to anastomose with the corresponding plantar metatarsal artery. 



(4) The first dorsal metatarsal artery is continued forwards from the dorsal artery 

 of the foot, and runs on the dorsal surface of the first dorsal interosseous muscle. It 

 ends by dividing into dorsal digital branches for the adjacent sides of the first and second 

 toes. Before it divides it usually gives off a dorsal digital branch which passes, deep to 

 the tendon of the extensor hallucis, to the medial side of the great toe. 



(5) The profunda branch passes through the posterior end of the first intermetatarsal 

 space, between the two heads of the first dorsal interosseous muscle, to the plantar aspect 

 of the foot, where it unites with the lateral plantar artery and completes tne plantar arch. 

 As it unites with the lateral plantar artery it gives off the first plantar metatarsal 

 artery (O.T. arteria magna hallucis), which passes forwards, along the first intermetatarsal 

 space, to the base of the first interdigital cleft, where it divides into plantar digital arterie 

 for the adjacent sides of the great and second toes ; before it divides it gives off a plantar 

 digital artery to the medial side of the great toe. 



VEN^E. 



. Veins commence at the terminations of the capillaries. They converge towards 

 the heart, and unite with one another to form larger and still larger vessels, until, 

 finally, seven large trunks are formed which open into the atria of the heart. 

 Three of the trunks, the superior vena cava, the inferior vena cava, and the coronary 

 sinus, belong to the systemic circulation ; they contain venous blood, and open into 

 the right atrium. The remaining four, the pulmonary veins, belong to the pulmonary 

 circulation ; they return oxygenated blood from the lungs, and' open into the left 

 atrium. 



In addition to the systemic and pulmonary veins, there is also a third group of 

 veins, constituting the portal system, in which blood from the abdominal part of 

 the alimentary canal, and from the spleen and pancreas, is conveyed to the liver. 

 The portal system is further peculiar in that it both begins and ends in capillaries. 

 From its terminal capillaries in the liver the hepatic veins arise, and as these open 

 into the inferior vena cava the blood of the portal system is finally poured into the 

 general systemic circulation. The hepatic veins also receive blood 'supplied to the 

 liver by the hepatic arteries. 



VEN.E PULMONALES. 



The terminal pulmonary veins (Figs. 750 and 757), two on each side, open into 

 the left atrium of the heart. Their tributaries arise in capillary plexuses in the 

 walls of the pulmonary alveoli. By the union of the smaller veins larger vessels 

 are formed which run along the anterior aspects of the bronchial tubes, and, uniting 

 together, ultimately form a single efferent vessel in each lobe, which passes into the 

 root of the lung. Thus there are five main pulmonary veins, but, immediately 

 after entering the root of the lung, the vessels from the upper and middle lobes of 

 the right lung join together, and so only four terminal pulmonary veins open into 

 the left atrium of the heart. Neither the main stems nor their tributaries possess 

 valves. 



Relations. In the root of the lung the upper pulmonary vein, on each side, lies 

 below and in front of the pulmonary artery. The lower pulmonary vein, on each 



