This is looking south along the communication gallery of the southwest wall--smaller arches that connect the bigger casemates like hallways. These are 10 feet across; the larger ones span 30 feet.
I've mentioned the 1916 blasting project in which Engineers used dynamite to knock down some of the brickwork on top of the fort to open up lines of sight for Battery Pensacola.
Most of the arches along the South Wall collapsed; those along the Southwest Wall here cracked through and through along the entire length of the wall.
As a little bonus, if you click on the pic to get the enlarged version, you can see the gap that was designed into the North, South, Northwest & Southwest walls between the big arch and the curtain wall. This allowed one or the other to settle without damaging the neighboring structure. It also allowed one or the other to be damaged or even to collapse without taking the entire section of wall down.