Sentence:  With respect to measurement, it would be advisable to take the circumference of the foot by placing the beginning of an inch tape measure a little beyond the great toenail, as the second toe is naturally the longest, passing the measure round the <WSD>protuberating</WSD> part of the heel, and bringing it up to the point of the beginning of the measure at the toe. 
Meaning of the word marked with <WSD> tags:  To bulge outward, producing a rounded protuberance.