I just had to find out, so I did what any researcher would, and fired up
DuckDuckGo and did an image search. ANd sure enough the book exists, and I found a copy of this print. If you doubt me,
look here or here.
The poem in full reads
NEW FEATS OF HORSEMANSHIP
Well mounted on a mettled steed,
Famed for his strength as well as speed,
Corrina and her favorite buck
Are pleased to have a flying f---k.
While o'er the downs the courser strains
With fiery eye, and loosened reins
Around his neck her arms she flings
Behind her buttocks move like springs
While Jack keeps time to every motion
And pours in love's delicious potion.
To be sure, this looks like a dangerous pastime, that worried-looking "young gentleman" could end up with a fractured penis, and that doesn't sound very nice, does it? Come to think of it, Corrina doesn't look too happy either.