He right and left coronary arteries the right and left coronary arteries supply blood to the pericardial sac drain into the right atrium branch from the aortic arch drain into the coronary sinus supply blood to the heart muscle itself

Superior Vena Cava

main vein; carries/drains deoxygenated blood from head, neck, shoulders into right atrium; located to the right of the aorta

- Two main tributaries that drain into it:

- Right brachiocephalic vein

- Left brachiocephalic vein

Inferior Vena Cava

carries/drains deoxygenated blood from the abdomen into the right atrium; enters the right atrium from the inferior side

Pulmonary Veins

carry oxygenated blood into the left atrium on posterior aspect; only veins that carry

oxygenated blood; four total

supplies blood to the heart itself

-Left Coronary Artery

-Right Coronary Artery

Arteries of the Heart

Left coronary artery

its branches supply:

- Left atrium

- Most of the left ventricle

- Some of the right ventricle

- Interventricular septum

- SA node (40% of people) (sinoatrial node)

stimulus is a change in the environment that causes an organism to react. the response is the reaction to the stimulus. some examples of stimuli for zebras are drought, to many predators, and bad feeding grounds such as dead grass or plants. zebras respond to stimuli just like all other living organisms

the oldest known insects are believed to live around 400 millions ago as suggested by the fossil records.   some plants having woody stems also evolved during this time.

after the evolution of insects the first four legged species or the tetrapods evolved in shallow freshwater habitats from the intermediate species approximately 397 million years ago. the tetrapods went on conquering the land giving rise to amphibians, reptiles, mammals and birds.

the major split in tetrapods first occurred 340 million years ago branching off from amphibians.

363 million years ago when the carboniferous period began the insects started roaming on land and taking flights, following which the four limbed tetrapods adapted in the terrestrial habitat.