Now we’ll move on to look at the principal veins of the thorax. We’ll look at the two largest veins in the body, the superior and inferior vena cava, which enter the thorax from above and below, and empty into the right atrium of the heart through two separate openings. We’ll also see the veins of the wall of the thorax, the azygos veins. We’ll start by looking at the major veins which contribute to the superior vena cava, the subclavian and internal jugular veins.
On each side, the subclavian vein, the principal vein of the upper extremity, joins with the internal jugular, the principal vein of the head and neck, here, behind the medial end of the clavicle, forming the brachiocephalic vein. The two brachiocephalic veins enter the thorax and unite, forming the superior vena cava.
To see the subclavian and internal jugular veins, we’ll remove the major muscles which lie in front of them - the pectoralis major, and sternocleidomastoid muscles.
Here’s the subclavian vein, coming up from beneath pectoralis minor, and passing beneath the clavicle. Here’s the internal jugular vein, with the omohyoid muscle in front of it. To see where these two veins join, we’ll remove the clavicles.
The subclavian vein passes over the flat, anterior part of the first rib. The anterior scalene muscle separates the subclavian vein from the subclavian artery. The dome of the pleura is just behind and beneath the subclavian vein. The internal jugular vein lies in front of the common carotid artery and lateral to it.
18.104.22.168 On each side the subclavian and internal jugular veins unite, to form the right and left brachiocephalic veins. The two brachiocephalic veins pass downwards into the thorax behind the manubrium. To follow them, we’ll remove the anterior chest wall, as we did before.
The lungs and the pericardium have also been removed. The cut ends of the two first ribs are here, and here. Here are the two brachiocephalic veins, the right, and the left, joining to form the superior vena cava. The superior vena cava lies well to the right of the mid-line. Because of this the right brachiocephalic vein is short, and runs straight downwards; the left one is longer, and runs quite obliquely.
The superior vena cava passes straight downwards, entering the pericardial sac here. To its left is the ascending aorta. Behind it is the trachea. The superior vena cava ends here by entering the highest part of the right atrium of the heart. The azygos vein, which we’ll see in a minute, joins the vena cava from behind, just before the vena cava enters the pericardium.