Final answer:
The subject of the description is Human Liver Anatomy.
Step-by-step explanation:
The subject of the description, "Centrally is the right portal vein and left portal vein. Anterior to this are segments (7, 8, and 4a), posterior to this are segments (6, 5, and 4b)" is Human Liver Anatomy.
The description is referring to the location of the portal veins in the liver and the segments anterior and posterior to them. The portal veins play a crucial role in supplying the liver with blood and nutrients from the digestive system.
Understanding human liver anatomy is important to comprehend the liver's functions and its role in processing and metabolizing bloodborne nutrients and toxins.