The flowerhead is arranged like a herring bone. The 'ribs' alternate while the 'backbone' veers sinuously from side to side between the individual flowers. I tried sketching the ligule (left), the straplike membrane in each leaf joint, but this one doesn't quite look like the perfect example in the book. The Reader's Digest Field Guide to the Wild Flowers of Britain describes the ligule as 'short, membranous'. The base of the leaf-blade 'has two claw-like lobes clasping the stem'. I'm going to have to keep sketching these little details to really get my eye in.
Italian Ryegrass is a similar species that is often planted, but I can tell this is our native Perennial Ryegrass because, in the Italian version, each flowerhead has a projecting bristle. These bristles are botanically known as awns, which comes from a Viking word for 'husk' or 'chaff'.
Related LinkPerennial Ryegrass International Forage Factsheet.