586 THE VEINS 



below the termination of the posterior vena cava and is covered in part by a 

 thin layer of ventricular muscle-fibers. It opens into the right atrium just below 

 the posterior vena cava. It is formed by the union of two tributaries. The great 

 cardiac or left coronary vein {Y. cordis magna) begins at the left side of the apex 

 of the heart, ascends in the k^ft longitudinal groove and turns l^ackward in the 

 coronary groove, in which it winds around the posttn-ior border of the heart to the 

 right side and joins the coronary sinus. The middle cardiac or right coronary vein 

 (V. cordis media) begins on the right side of the apex, ascends in the right longitu- 

 dinal groove and joins the coronary sinus, or opens separately into the atrium just 

 in front of the orifice of the left vein, so that a common trunk (coronary sinus) 

 does not then exist. 



The small cardiac veins (Xv. cordis minores), three to five in number, are 

 small vessels which return some Ijlood from the right ventricle and atrium; they 

 open into the latter near the coronary groove in spaces between the musculi 

 pectinati. 



THE ANTERIOR VENA CAVA (Fig. 429) 



The anterior vena cava (V. cava cranialis) returns to the heart the blood from 

 the head, neck, thoracic limbs, and the greater ])art of the thoracic wall. It is 

 formed at the ventral part of the thoracic inlet by the confluence of the two jugu- 

 lar and two brachial veins. Its origin is attached to the first pair of ribs. It 

 passes backward in the anterior mediastinum, at first median and ventral to the 

 common carotid trunk, then deviates to the right of the anterior aorta, and opens 

 into the right atrium opposite to the third rib. The demarcation between vein and 

 atrium is not very distinct. It contains no valves except at the mouths of its 

 radicles. Its length is about five to six inches (ca. 12 to 15 cm.) and its caliber about 

 two inches (ca. 5 cm.) in a subject of medium size. Its right face is crossed by 

 the right phrenic nerve, and on the left it is related to the anterior aorta and brachio- 

 cephalic artery. It receives, in addition to small pericardial and mediastinal 

 veins, the following tributaries: 



1. The internal thoracic vein (V. thoracica interna) is a satellite of the artery 

 of that name. It opens into the anterior vena cava at the first rib. 



2. The vertebral vein (V. vertebralis) corresponds to the homonymous artery. 

 On the right side it terminates either in front of the deep cervical vein or by a short 

 common trunk with it. On the left side it almost always unites with the deep 

 cervical and vertebral vein to form a common trunk. 



3. The deep or superior cervical vein (V. cervicalis profunda) corresponds to 

 the artery. On the right side it leaves the artery at the first intercostal space, 

 crosses the right face of the trachea and opens into the vena cava; it may form a 

 common trunk with the dorsal or vertebral. On the left side there is nearly always 

 a common trunk for all three. 



4. The dorsal vein (V. costo-cervicalis) corresponds to the artery. On the 

 right side it leaves the artery on entering the thorax, crosses the right face of the 

 trachea, and opens into the vena cava in front of the deep cervical or by a common 

 trunk with it. On the left side it almost always joins the deep cervical and verte- 

 bral to form a short common trunk which crosses the left face of the intrathoracic 

 part of the brachial artery opposite the second rib and opens into the anterior vena 

 cava. 



The Vena Azygos 



The vena azygos (Fig. 429) is an unpaired vessel which arises at the level of 



the first lumbar vertebra by radicles coming from the psoas and the crura of the 



diaphragm; it is connected with the first lumbar vein. It passes forward along 



the right side of the Ijodies of the thoracic vertebrae, in contact usually with the 



