1. Heart, right ventricle. 2. Heart, left ventricle. 3. Heart, left auricle. 4. Pulmonary artery. 5. Pulmonary veins. 6. Anterior aorta. 7. Carotid artery. 8. Glosso-facial artery. 9. Left brachial artery. 10. Dorsal artery. 11. Superior cervical artery. 12. Vertebral artery. 12´. Internal thoracic artery. 13. Humeral artery. 14. Radial artery. 14´. Cubital artery. 15. Great metacarpal artery. 16. Ungual branches. 17. Posterior aorta. 18. Coeliac axis. 19. Mesenteric arteries. 20. Renal artery (left). 21. Small testicular artery. 22. Posterior vena cava. 23. Portal vein. 23´. Hepatic circulation. 24. External iliac artery. 25. Internal iliac artery. 26. Lateral sacral artery. 27. Femoral artery. 28. Posterior tibial artery. 28´. Anterior tibial artery. 28´´. Femoro-popliteal artery. 29. Metatarsal vessels. 30. Venous plexus of the foot. 31. Internal saphenic vein. 32. Cephalic vein. 33. Jugular vein. ARTERIES.--Arteries are tubes the purpose of which is to convey the blood from the heart. For this reason it is apparent that all arteries carry pure arterial blood with but one exception. The pulmonary artery carries the blood from the right ventricle to the lungs, and consequently carries impure or venous blood. Each time the left ventricle contracts it causes a wave, as it were, to pass all through the arteries. This contraction takes place when in a healthy condition about 36 to 42 times every minute and gives rise to what is known as the pulse. This wave, or beating, may be detected at any point where the artery is situated so closely to the surface as to affect the outside of the body sufficient to be felt by placing the finger on the point; consequently the pulse may be counted at any of these points. Place your forefinger on the lower edge of your own lower jaw directly under the corner of your mouth. At this point an artery passes out over the jaw bone and therefore runs very close to the surface, making it quite possible to feel the wave caused by the contraction of your own heart, quite distinctly. Near this point on the jaw of the horse the pulse is most conveniently felt and counted. The walls of the arteries are composed of elastic tissue and after death are always lying open. Blood is never found in them after death because they continue to contract sufficiently long enough to force all the blood through them. VEINS.--Veins are tubes in construction not so strong as the arteries--the purpose of which is to convey the blood from all parts of the body to the heart. The heart wave does not affect the veins, and consequently the pulse cannot be detected by placing the finger on an exposed portion of one of them. It is also apparent that all veins carry impure or venous blood with but one exception, viz., the pulmonary vein, the purpose of which is to conduct the purified blood from the lungs to the heart.