Question: What was the subject of the cameo that appears to have been the inspiration for Michelangelo's "Creation of Adam"?
About the article "The Creation of Adam", section "Miscellany".

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Michelangelo's main source of inspiration for his Adam in his "Creation of Adam" seems to have been a cameo showing a nude Augustus Caesar riding sidesaddle on a Capricorn.
This cameo is now at Alnwick Castle, Northumberland.
The cameo used to belong to cardinal Domenico Grimani who lived in Rome while Michelangelo painted the ceiling.
Evidence suggests that Michelangelo and Grimani were friends.
The only parts of Michelangelo's Adam that could not have been borrowed from this cameo are his right hand and arm; this may explain why Michelangelo had to draw Adam's right hand and arm three times when he made the drawing for Adam that is now in the British Museum.
Some scholars have been dissatisfied with the theory Michelangelo was mainly inspired by Lorenzo Ghiberti's Adam in his "Creation of Adam".
This cameo offers an alternative theory.
God is depicted as an elderly white-bearded man wrapped in a swirling cloak while Adam, on the lower left, is completely nude.
God's right arm is outstretched to impart the spark of life from his own finger into that of Adam, whose left arm is extended in a pose mirroring God's, a reminder that man is created in the image and likeness of God ().
Another point is that Adam's finger and God's finger are not touching.
It gives the impression that God, the giver of life, is reaching out to Adam who receives it; they are not on "the same level" as would be two humans shaking hands, for instance.
Many hypotheses have been formulated regarding the identity and meaning of the figures around God.
The person protected by God's left arm might be Eve due to the figure's feminine appearance and gaze towards Adam, but was also suggested to be Virgin Mary, Sophia, the personified human soul, or an angel of feminine build.
"The Creation of Adam" is generally thought to depict the excerpt "God created man in his own image, in the image of God he created him" ().
The inspiration for Michelangelo's treatment of the subject may come from a medieval hymn called "Veni Creator Spiritus", which asks the 'finger of the paternal right hand' ("digitus paternae dexterae") to give the faithful speech. 
Several hypotheses have been put forward about the meaning of "The Creation of Adam"'s highly original composition, many of them taking Michelangelo's well-documented expertise in human anatomy as their starting point.
In 1990, an Anderson, Indiana physician named Frank Lynn Meshberger, M.D.
noted in the medical publication the "Journal of the American Medical Association" that the background figures and shapes portrayed behind the figure of God appeared to be an anatomically accurate picture of the human brain.
Dr. Meshberger's interpretation has been discussed by Dr. Mark Lee Appler.
On close examination, borders in the painting correlate with major sulci of the cerebrum in the inner and outer surface of the brain, the brain stem, the frontal lobe, the basilar artery, the pituitary gland and the optic chiasm.
Alternatively, it has been observed that the red cloth around God has the shape of a human uterus (one art historian has called it a "uterine mantle"), and that the scarf hanging out, coloured green, could be a newly cut umbilical cord.
"This is an interesting hypothesis that presents the Creation scene as an idealised representation of the physical birth of man.
It explains the navel that appears on Adam, which is at first perplexing because he was created, not born of a woman."
Masaccio provided a large inspiration to the more famous Renaissance painter Michelangelo, due to the fact that Michelangelo's teacher, Domenico Ghirlandaio, looked almost exclusively to him for inspiration for his religious scenes.
Ghirlandaio also imitated various designs done by Masaccio.
This influence is most visible in Michelangelo's "The Fall of Man and the Expulsion from the Garden of Eden" on the ceiling of the Sistine Chapel. 
The missing depth is not the only factor that the critics deplore.
An important feature of Michelangelo's work which, in many places, has disappeared forever is the painting of the eyeballs.
Eyes appear in many instances to have been painted "buon fresco".
Wherever they have not been painted buon fresco but added "a secco", they have been removed by the restorers.
They are an essential part of the most impressive and famous of the frescoes, the "Creation of Adam".
Adam gazes at God.
God looks directly at Adam.
And under God's protective arm, Eve turns her eyes sideways in a look of admiration for her husband-to-be.
Again and again, Michelangelo painted telling gazes into the faces of his characters.
The eye sockets of the family in the Zorobabel lunette are empty as are the eyes of the man in the Aminadab lunette, but the removal that has caused the most distress to the critics are the eyes of the little figure in green and white who once looked out of the gloom above the lunette of Jesse.
Arguimbau says:Richard Serrin, in an essay entitled "Lies and Misdemeanors, Gianluigi Colalucci's Sistine Chapel Revisted" says: