IXyOMLXA TIC H05 



clavicular articulation on the left side to the lower liorder of the first costal carti- 

 lage at its junction with the sternum on the right side, will indicate its course. 

 The left innominate vein is on a level with the top of the sternum at hirth. 



Relations. — In front, in addition to the manubrium of the sternum, it has the 

 origins of the sterno-liyoid and sterno-thyroid muscles, and the remains of the 

 thymus gland, the sternal end of the left clavicle, and the sterno-clavicular articu- 

 lation (figs. 828, 381a). 



Behind, are the three chief arteries arising from the arch of the aorta, the 

 trachea, and the left phrenic and left pneumogastric nerves. 



Below it is the transverse portion of the arch of tlie aorta. 



Above it are the cervical fascia and inferior thyroid veins. 



Tributaries. — In addition to the internal jugular and subclavian veins, by the 

 contiuence of which the innominate veins are formed, each vein receives on it^ 

 uj)per aspect the vertebral, the deep cervical and inferior thyroid veins; and on its 

 lower aspect the internal mammary vein. The left vein, moreover, is joined by 

 the left superior intercostiil, and by the thymic, mediastinal, and jjericardiac veins. 

 At the confluence of the internal jugular and subclavian veins on the right side, 

 the right lymphatic duct opens; on the left side the thoracic duct. The vertebral, 

 the deep cervical, and the inferior thyroid veins are described with the deep veins 

 of the head and nock (])age 628). 



The internal mammary veins (fig. 344) are formed l)y the union of the 

 vente comites of the superior epigastric and musculo-phrenic Itranches of the inter- 

 nal mammary artery. They receive in their course through the chest collateral 

 trilnitaries corresponding to the l>ranches of the internal manunary artery. Just 

 l>efore reaching the innominate vein they unite behind the first interct)Stal space 

 to form a single trunk which opens into the innominate vein on the inner side of 

 the internal mammary artery. They contain many valves. 



The left superior intercostal vein — or, more correctly speaking, the lower left 

 su)ierior intercostal vein — longer than the right, which is described as a tributary 

 of the vena azygos major, receives the intercostal veins from the three or four upper 

 left intercostal spaces except from the first space, and, ascending over the arch 

 of the aorta, opens into the left innominate vein. It usually receives the left 

 bronchial vein, and communicates with the upper left azygos vein. (See Inter- 

 costal ^'EIXS. page (308. ) 



Thi- mediastinal, pericardiac, and thymic veins are small vessels, correspond- 

 ing to the arteries of those names given off by the internal mammarv. They do 

 not, however, as a rule, join the internal mammary vein, but unite into a single 

 trunk (figs. 317, 382), which passes over the transverse part of the arch of the aorta, 

 and opens into the lower and anterior part of the left innominate vein. 



Chief Variations in the Superior Vena Cava and Innominate Veins 



Tlie variations in the vena cava and innominate veins depend upon certain abnormalities in 

 the development of the frreat veins from the ducts of Cuvier and the primitive jugular veins, 

 and can here receive only a brief mention. They may be classified as follows : — 



(1) Variations due to the Persistence of the Left Duct <f Cuvier 



(a) The left subclavian may join the left internal jugular vein to form a trunk which is con- 

 tinued almost vertically downwards over the arch of the aorta in front of the root of the left lung, 

 to open into the coronary sinus of the heart. Tliis variety is known as the persi.^tent left superior 

 vena cava, and is the normal arranL'einerit of tlie great anterior veins in some animals. The rudi- 

 ments of this vein are found in Man in the so-called ohli(|ue vein of Marshall, which stretches 

 from the cijronary sinus through the vestigial fuld of the peric.ndium, and is often continued as 

 a fine fibmus cord to the su|ierior intercostal vein. 



When the so-called left superior vena cava is present, the upper left azygos vein (the remains 

 of the left primitive cardinal vein) may open into it hy archiiiL' over the rout of the left luiiir in 

 a way similar to that in which the greater azj'gos (the right primitive cardinal vein) opens into 

 the superior vena cava over the root of the right lung. The normal left innominate vein may 

 be absent, or may be quite small or rudimentary, the resvilt of the non-development, or oidy 

 partial development, of a transverse l)ranch (which becomes the left intii'minate) when the left 

 part of the sinus venosus and the left duct of Cuvier are transformed into the coronarj" .sinus, 

 the oblique vein of Marshall, and the upper jiortion of the left suj)erior intercostal vein. 



