The notion that man besides his physical body also possesses subtle anatomy is central to contemporary holistic spirituality and Esotericism as well as to alternative medicine and Modern Yoga. Concepts related to subtle anatomy can historically be found in religious traditions worldwide. However, the contemporary “Western” subtle anatomy has a relatively standardized sevenfold structure, linked to seven chakras, described as subtle energy centers in the human body. The article discusses a central period in the late 19th century when the Theosophical Society and its most significant forefront, Helena Petrovna Blavatsky, presented the concept of subtle anatomy to a broader Western audience. It also deals with the question of how the doctrine of three human principles (body, soul, and spirit) developed into her teachings of the seven human principles. A change took place around 1880-81, in an interaction between American, European, and Indian theosophists, and there is a shift of doctrine between Blavatsky's two major works Isis Unveiled (1877) and  The Secret Doctrine  (1888) where the latter contains her sevenfold cosmology in total. In Modern Yoga, the doctrine of subtle anatomy is usually linked to Eastern traditions, especially Hinduism, but how important was the Theosophical Society’s move to India in terms of changing Blavatsky’s teachings of the human principles? Was it the exchange of ideas with Hindus and Buddhists that initiated its development? The article explores another hypothesis which instead traces Blavatsky’s teachings about the seven principles back to influences before the move to India, as well as to specific numerological, mathematical and geometric speculations that she shared with several thinkers in her time. Similar ideas in New Age literature would go as “Sacred Geometry.” The article presents arithmological conceptions that were common among late 19thcentury occultists, spiritualists, and “mythographers.” These include in particular: The number seven, Pythagoras tetraktys, the tetrad, the pyramid, the cube, and the hexagram.