THE SUPERIOR CAVAL SYSTEM. 



857 



Variations. — The principal variations which occur in connection with the cardiac veins have 

 been noted in the description of the vessels, and it need only be added that the oblique vein of 

 the left auricle is not infrequently entirely lacking, except in so far as it is represented by a 

 fibrous cord, that absence of the great coronary vein has been observed, and that the middle 

 vein occasionally opens directly into the right auricle. 



THE SUPERIOR CAVAL SYSTEM. 



The Vena Cava Superior. 



The superior or descending vena cava (Figs. 749, 751) is the main venous trunk 

 which delivers to the heart the blood returning from the head, neck, upper limbs, and 

 thorax. It measures 7-8 cm. (3 in. } in length, and has a diameter at its termination 

 of about 2. 2 cm. (a little less than i in. ). It is situated throughout its entire course in 

 the thoracic cavity, lying in the superior mediastinum, and is formed immediately 



Vertebral vein 



Fig. 751. 



Anterior jugular 

 Transverse cervical v 

 Clavicle, cut 

 Suprascapular vein 



Right inferior 



thyroid vein 

 I. right posterior 



intercostal vein* 



Internal 



' mammary vein 



Right 



innominate vein' 



Superior vena cava' 



Di 



right 



A pulmonary vein 



Right 



auricular appendix 



Right coronary or 

 small cardiac vein 



Right lung, 



mesial surface 



Left internal jugular vein 

 Scalenus anticus muscle 

 External jugular vein 



Left subclavian vein 

 Clavicle 



Left inferior thyroid vein 

 I. rib 



Left innominate vein 

 ■Superior intercostal vein 

 I. left posterior intercostal 

 4 _ [vein 



^Internal mammary vein 



Aorta 



Line of pericardial reflection 



R. and L. pulmonary arteries 

 A division of left bronchus 



Pulmonary artery 



Left pulmonary vein 



Bronchus 



Left auricular appendix 



Left coronary or great 

 cardiac vein 



Left lung, mesial surface 



Diaphragm, thoracic surface 



Xii^ 



Dissection showing innominate veins and superior vena cava in position; 

 lungs have been pulled aside. 



below the lower border of the first costal cartilage of the right side by the union of the 

 right and left innominate (brachio-cephalic) veins. Its course is downward and 

 slightly backward, with a curvature corresponding to the first portion of the arch of 

 the aorta, with which it is in relation. Below, it opens into the upper posterior portion 

 of the right auricle on a level with the third costal cartilage of the right side. 



Relations. — The lower portion of the superior vena cava is invested by the peri- 

 cardium to an extent varving from a few to 40 mm. , on an average, perhaps to about 

 one-third its length. The upper extrapericardial portion is in relation anteriorly 



