carotid endarterectomy

what is the first muscle layer and what is its function:
Platysma and facial expression
What animal has the biggest platysma:
Horse
What is the first branch of the external carotid
superior thyroid.
Why is it ok to occlude one internal carotid.
Circle of Willis gets blood to the contralateral brain.

thyroidectomy pimp quesions

What it the vascular supply of the thyroid:
Superior thyroid(branch of external carotid)
inferior thyroid(branch of thyrocervical trunk)