Wiktionary
deltoideus
a. Like a triangle, triangular. n. Short for deltoideus muscle much as deltoid is used as short for deltoid muscle.
WordNet
Usage examples of "deltoideus".
The deltoideus, triceps brachia, latissimus dorsi and trapezius are like great marvelous wads of brown weathered stone.
He was moaning and crying out so loudly that she double-checked her readings—but the tricorder indicated only minor damage to his right deltoideus muscle.