Sentence:  As we age, the major arteries of our bodies frequently become thickened with plaque, a fatty material with an oatmeal-like consistency that builds up along the <WSD>inner</WSD> lining of blood vessels. 
Meaning of the word marked with <WSD> tags:  Being or occurring (farther) inside, situated farther in, located (situated) or happening on the inside of something, situated within or farther within contained within something.