Hyleg:
A term used by ancient Arabian Astrologers to designate the points in the horoscope which are the principal foci of vitality and healthy, namely the Sun, Moon and Ascendant.
It needs but little argument to show that the great and glorious reservoir of life which we call the Sun is an important factor in the matter of health, and that the lesser Light, the Moon, has dominion in this respect, for she collects and reflects the solar ray. And it is a matter of common knowledge that she is in some way connected with gestation, and parturition, therefore, the Moon is the particular significator of health in a woman's horoscope while the Sun has the strongest influence in a man's figure. Both are important however, for if, in a man's figure, Saturn is square to the Moon he will feel it, but if this configuration happens in a woman's horoscope, she will feel it more; and conversely, Saturn square to the Sun in a woman's horoscope will affect her health, but not in the same degree as it will that of a man when occurring in his figure.
The reason why the Ascendant is designated as a factor in health and vitality is not so apparent upon the surface, but when we realize that the ascendant at birth is the Moon's place at conception, the reason is obvious, for the Moon is the planet of fecundation, the focus and reflector of the solar Life-forces, and if, at the time of conception, when the human seed-atom was planted, she was in a weak sign like Virgo, there is a fundamental lack of energy and vitality at the very start of life, and a consequent lassitude which affects through all the years of its existence, the body then beginning to germinate.
Thus, to sum up, the Sun, Moon and Ascendant are all important significators of health and vitality for both sexes, but the position and aspects of the Moon are more important to a woman than those of the Sun and Ascendant, and the position and aspects of the Sun are more vital to the health of a man than the two other factors.
In modern times the word 'Hyleg,' and the designation of the vital parts of the horoscope as 'hylegiacal' places are not generally used. The writer always speaks of them as 'significance of health,' then everybody understands what is meant, and it seems senseless to befog the subject with mysterious terms when good, plain English conveys our meaning so much better. It should also be understood that to
judge any subject, be it health, wealth, joy or sorrow or any other thing that may befall, the special significators give only a limited amount of information. To obtain a really comprehensive knowledge each subject must be judged from the horoscope as a whole
Credit- art of astrology