Arnie may be right. But I get the impression (maybe I'm wrong) that this drawing shows a lower yard and mast of a square-rigged ship from the late eighteenth or early nineteenth century. (Warning: Charles Davis was notorious for injecting anachronisms into his drawings.) in that period the lower yard of a good-sized ship wasn't usually secured with a parrel, but with a simple rope truss. (HMS Victory and the USS Constitution are good examples.)
Aside: would you believe that when I tried to type "HMS," this infernal "smart phone tried to change it to "Hamas"? Heaven help us.
There are variations, but essentially a yard truss is a pair of heavy ropes secured to the yard on either side of the mast. Each of the lines has an eye spliced into one end. The other end passes behind the mast, goes through the eye in the end of the other line, and ends with a tackle that allows it to be hove taut or slacked off, thereby controlling the distance between the yard and the mast. I'm used to seeing simple, vertical tackles running straight to the deck. Davis shows them running along the yard. That would certainly work.
Ships of earlier years did use rib-and-bead parrels on their lower yards. As the nineteenth century went on, the truss tackle got replaced by an iron fitting (called a truss) that kept the yard a foot or two in front of the mast, so the yard could swing around without bumping into the shrouds. (Example: the Cutty Sark.)
I THINK Davis's goof was to show the yard passing in front of, rather than behind, the mast, so we seem to be looking at them from the front rather than the back. As he shows it, the lines he calls yard tackles (I'd call them truss tackles) are set up on the front of the yard. That wouldn't work.
Don is so right about the olde days when model mags published lots of drawings - many of them quite beautiful. In recent decades we've seen what I'm afraid is a last great flourishing of the traditional art of drafting. Twenty or thirty years ago the British monthly Scale Models regularly carried aircraft drawings by a man named Arthur Bentley that we're almost unbelievable in their detail, accuracy, and artistic subtlety. (More than once my copy of SM mysteriously vanished; my dad had taken it to work at the OSU School of Architecture to show the students just how good a drawing could be.) And some of the draftsmen responsible for the Anatomy of the Ship volumes ( I'm thinking of John McKay, John Roberts, and Janos Skulski in particular) are among the best ever. I'm not fit to sharpen their pencils. CAD is a wonderful thing, but I've shed more than one tear over the passing of a great art form. Nowadays, if I walk into the university bookstore and ask for a rapidograph tip, or a set of ship curves, or an adjustable triangle, the student/clerk looks at me as though I had two heads. And this phone tried to change "rapidograph" to "rapidly raspy."
The old master marine painters (the Van De Veldes, Robert Salmon, James Butterworth, Michel Corne, et al) actually were highly conscientious about rigging. The trouble is that almost every old painting we see today has been restored or repaired at least once - and restorers, trying to deal with chipped paint, cracks, and faded colors, frequently know nothing about rigging. I've seen more than one glaring error that turned out to be a blunder by some so-called restorer in the nineteenth century. Modern conservators are trained not to do stuff like that.
Sorry; too long as usual. But this is interesting stuff.