The Ossmodula, also called the Ironheart, is the 2nd of the 19 gene-seed organs implanted into a Space Marine Neophyte during the induction process to create a new Astartes. This implant, surgically placed alongside the Neophyte's pituitary gland at the base of the brain, thus becoming a part of the Space Marine's endocrine system, secretes a specially engineered form of human growth hormone. When the effects of this hormone are combined with a diet laced with microscopic ceramic-based minerals, they act to synthesise the rapid growth of an Astartes' skeletomuscular system which results in an Astartes' superhuman strength and massive size compared to a baseline human male. Two years after the surgery to implant the Ossmodula is completed, the Neophyte Space Marine's skeleton will be larger and exponentially stronger than a normal man's with growth having topped out at around 7-7.5 feet in height with an equivalent amount of skeleto-muscular mass. During this time the rib cage will fuse into a solid mass of bullet-proof, interlaced bone plates. The resulting structure protects the Space Marine's organs from damage in a way the normal human skeleton never could, though at the price of producing greater difficulties for the Chapter's Apothecaries when they must perform surgeries on a Space Marine's body cavity.
- Codex: Space Marines (5th Edition)