Democritus Junior to the Reader, page 18

[p. 18]
Saturn was the lord of my geniture, culminating, etc., and Mars principal significator of manners, in partile conjunction with mine ascendant; both fortunate in their houses, etc.

Burton was quite planet-struck. An Anglican priest, he first delved into astrology to prove it was false, but instead grew fascinated with it. His studies led him to align the four humors with astrology:

He noted that Saturn and Jupiter in conjunct with Libra tended to produce a mild melancholia, while Saturn and the Moon (rulers of opposite signs) conjunct in Scorpio made it severe. By contrast, a conjunction of the Moon and Mars in opposition to Saturn and mercury induced a manic condition; Venus in Leo in aspect to the Moon fostered lust; and an uncontrollable depravity resulted when Venus and Mercury were conjunct the ascendant, or Mercury conjunct the Moon.

Benson Bobrick, Fated Sky: Astrology in History (Simon & Schuster, 2005), pp. 175–6.

Burton's horoscope is reproduced in some editions of Anatomy; it served to calculate the exact date of his birth which had long been disputed. The horoscope copied above is based on the one drawn in Burton's hand, where the date is illegible, and it incorrectly assumes it to be 1576. It has now been established that the correct date is 1577.

If you look at the frontispiece, it too is full of astrological symbols which correspond to each type of melancholy. 

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Minerva's tower...

Minerva, the Roman goddess of wisdom, intelligence, the arts. I understand Minerva's tower to roughly mean what nowadays we designate as the "ivory tower," albeit the origins of the two phrases are different (the latter phrase was coined by Sainte-Beuve).

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Burton's footnote "Hensius Primerio" does not mean, as I thought at first, "Hensius the First," or the elder Hensius, but, as Edward Bensly notes (Notes & Queries, 10th ser., vol. II, Aug. 13, 1904, p. 124), still rather cryptically to my taste, Daniel Hensius's (1580-1655) letter to one Jacobus Primerius to be found in an opuscule entitled Laus Asini of 1629. (Which would then mean this reference was a later addition?) 

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... ipse mihi theatrum [a theatre unto myself] 
... A mere spectator of other men's fortunes and adventures, and how they act their parts, which methinks are diversely presented unto me, as from a common theatre or scene. ...

All these references to theatre bring to mind the melancholy Jaques's monologue in As You Like It, 

                All the world's a stage,
And all the men and women merely players;
They have their exits and their entrances;
And one man in his time plays many parts,
His acts being seven ages.