The Magnificat, also called The Amplifier, is one of the twenty-two gene-seed implant organs of the Adeptus Astartes, and one of the three unique only to the Primaris Space Marines. A small, thumbnail-sized lobe that is inserted into the brain's cortex, the Magnificat secretes hormones that increase the body's growth functions whilst also intensifying the function of its other transhuman implants, especially those of the Biscopea and the Ossmodula.
The result is to produce an Astartes who is physically even larger, stronger and with faster reaction times than his non-Primaris brethren, often growing up to a Terran foot taller with an equivalent increase in skeleto-muscular mass.
In truth, the Magnificat is but half of the true, dual-valve Immortis Gland (the so-called God-Maker) that the Emperor created for His Primarchs. However, Archmagos Belisarius Cawl, who oversaw the project to create Primaris Astartes after the end of the Horus Heresy, could only find materials and genetic blueprints to build the Dextrophic Lobe (the right half of the Immortis Gland), while plans for the Sintarius (the left half) that would complete the original super-organ had been wholly eradicated from Imperial records of the Primarch Project. Whether this was done by the Emperor's own hand or by some nefarious source, Cawl could not tell.
- Codex: Adeptus Astartes - Space Marines (8th Edition), "The Making of a Space Marine", pp. 10-11