The arteries are the bloodvessels which leave the heart and break up into capillaries for the supply of the tissues. There are two systems of circulation- the pulmonary, consisting of the pulmonary artery leaving the right ventricle and ending in the pulmonary veins which enter the left auricle;. and the systemic, consisting of the aorta leaving the left ventricle and ending in the superior and inferior venae cavae which enter the right auricle.

Fig. 56. - The Aorta in the Thorax, and the Principal Arteries of the Head and Neck

1. Arch of the Aorta

2. Aortic Isthmus

3. Aortic Spindle

4. Descending Aorta

5. Coronary Arteries (from Ascending Aorta)

6. Innominate Artery

7. Left Common Carotid

8. Left Subclavian

9. Right Common Carotid

10. Right Subclavian 11. External Carotid

12. Internal Carotid

13. Internal Maxillary

14. Superficial Temporal

15. Vertebral

16. Internal Mammary

17. Thyroid Axis

18. Inferior Thyroid

19. Transverse Cervical

20. Suprascapular

21. Superior Thyroid

22. Lingual

23. Facial

24. Occipital

25. Posterior Auricular

26. Ascending Pharyngeal

27. Transverse Facial

28. Aortic Intercostals

Pulmonary artery

The Pulmonary artery arises from the base of the right ventricle of the heart. It is a short vessel about 2 inches long. It passes upwards to the left of the ascending aorta, and terminates by dividing into right and left pulmonary arteries, which enter the roots of the right and left lungs respectively.

Aorta

The Aorta rises from the base of the left ventricle of the heart. It passes upwards, backwards, and to the left, forming an arch, which, on reaching the vertebral column, passes downwards as far as the body of the fourth lumbar vertebra, where it terminates by dividing into the two common iliac arteries. For convenience of description it is divided into four parts : (1) The ascending aorta, (2) the arch of the aorta, (3) the descending thoracic aorta, (4) the abdominal aorta.

Fig. 55. - The Aorta.

The Ascending Aorta arises from the base of the left ventricle opposite the lower border of the third left costal cartilage. It passes upwards, forwards, and to the right, terminating in the arch of the aorta at the level of the junction of the right second costal cartilage with the sternum.

Branches

Right and left coronary arteries, which supply the heart muscle.

The Arch of the Aorta lies behind the lower part of the manubrium, and begins at the termination of the ascending aorta, terminating as the descending aorta opposite the lower border of the body of the fourth dorsal vertebra. The arch passes upwards, backwards, and to the left in front of the trachea, and curving over the pulmonary artery; it then passes backwards to the left of the trachea and turns downwards.

Branches of the Arch of the Aorta supply the head and neck and upper limb. The branch on the right side- the innominate artery - is a very short trunk, which divides almost at once into right common carotid and right subclavian arteries; the left common carotid and left subclavian arteries are given off from the arch itself.

The Descending Aorta extends from the termination of the arch at the fourth dorsal vertebra, and ends at the opening in the diaphragm opposite the twelfth dorsaA vertebra, by becoming the abdominal aorta. It lies on the vertebral column and is in contact anteriorly with the root of the left lung, the pericardium the oesophagus, and the crura of the diaphragm.

The branches are divided into two sets, visceral and parietal, supplying the muscles of the thorax and its contents.