510 THE SUPERIOR VENA CAVA. 



The coronary sinus is about an inch in length, and is placed at the back of 

 the heart, in the groove between the left auricle and ventricle, where it is covered 

 by the muscular fibres of the auricle. At its termination it opens into the right 

 auricle, immediately in front of the inferior vena cava, and its orifice is covered by 

 the Thebesian valve. The sinus is joined by the principal veins of the heart in the 

 manner described above, and also at its left extremity by a small straight vein 

 (pUique vein of Marshall) which runs downwards and inwards over the back 

 of the left auricle. All the veins joining the sinus, except the small oblique 

 vein which is often imperforate, are provided with more or less complete valves at 

 their terminations. 



The anterior cardiac veins are two or three small vessels running upwards on 

 the front of the right ventricle, and one of larger size ascending along the right 

 border of the heart, all of which open into the auricle immediately above the 

 auriculo-ventricular groove. These veins have no valves. 



The smallest cardiac veins (vense cordis minimse), very variable in number, 

 are contained in the substance of the heart, and open into the right auricle, 

 especially upon and in the neighbourhood of the interauricular septum, giving rise 

 to some of the foramina Thebesii. Similar minute veins open into the left auricle, 

 and according to L. Langer also into both ventricular cavities. 



The coronaiy sinus, together with the small oblique vein, considered with reference to 

 their foetal condition and certain abnormal conditions to which they are subject along with 

 other neighbouring veins, may be looked upon rather as the persistent terminal parts of a 

 typically distinct left superior vena cava (duct of Cuvier, with the left horn and transverse 

 part of the sinus venosus), than as simply the main stem of the cardiac veins. 

 The explanation of this will be found in the description of the development of these veins 

 in Vol. I. 



SUPERIOR VENA CAVA. 



The superior or descending vena cava conveys to the heart the blood which is 

 returned from the head and neck, the upper limbs, and the walls of the thorax. It 

 is formed by the union of the right and left innominate veins, behind the junction 

 of the first costal cartilage of the right side with the sternum, and descends nearly 

 vertically to the base of the heart, where it opens into the right auricle, opposite 

 the third costal cartilage. It is about three inches long, and in its course it describes a 

 slight curve, the convexity of which is directed to the right side. It has no valves. 



At its commencement, the superior vena cava is placed on the right side of the 

 innominate artery, and rests against the beginning of the right bronchus, being 

 covered in front and externally by the pleura. The right phrenic nerve also lies 

 along its outer side. About an inch and a half above its termination, it perforates 

 the fibrous layer of the pericardium, the serous membrane being reflected over it and 

 surrounding it except along its posterior surface. The lower part of the vein lies 

 in front of the right division of the pulmonary artery and the upper right pulmonary 

 vein, and the ascending aorta is to its inner side. 



The superior vena cava receives small pericardial and mediastinal veins, and 

 immediately above the place where it perforates the pericardium it is joined by the 

 large azygos vein. 



INNOMINATE VEINS. 



The innominate or brachio-cephalic veins, commencing on each side by the 

 union of the subclavian and internal jugular veins behind the inner end of the 

 clavicle, transmit the blood returning from the head and neck, the upper limbs, and 

 a part of the thoracic wall. They end below by uniting to form the superior vena 

 cava, beneath the junction of the first costal cartilage of the right side with the 



