Is there a Caitian / Kzinti connection? Or are they just two completely different species of cat-people with no relation?
I don't know. Do you want a link to exist? I'm not typing that just to be flippant. Every Trek fan has his own ideas about that kind of thing. I remember some publications suggested they splintered from a common ancestor, others implied coincidental, parallel evolution. I suspect Larry Niven would like to keep them separate if only to avoid legal issues. But go with what you personally like.
What about that silly three-breasted cat creature in TFF?
From a totally personal and admittedly biased standpoint, silly is the operative word. I see her and all I can think about is the Mars colony hooker from "Total Recall". Please, someone correct me if I'm wrong, but wasn't the same make-up artist involved with both productions? I just don't see her as a Caitian, felinoid, yeah, but not a Caitian. The only fur she had was upon her scalp and tail. She had plantigrade feet. But if you see her as one, fine, doesn't bother me. Maybe she's yet another one of these cross-species offsprings that are never adequately explained in Trek. Or maybe she's the infamous Eccentrica Gallumbits, the triple-breasted wh*re of Eroticon 6 repeatedly mentioned in Douglas Adams' "Hitchhikers' Guide".
Wasn't there also a cat-person in ST IV?
Yes, actually two. They both appeared at Kirk's "trial". They appeared to have been cast from the same molds, but they had different hair applied. One had longer reddish fur with bobcat type cheek "tufts", while the other had short, black hair, suggesting more of a black leopard motif. Since we didn't see their feet, we can imagine they may have possessed digitigrade paws.
I'm curious about all types of Trek cat people.
One of the earlier Pocket Books novels, "Uhura's Song" featured two feline species with a common history. Uhura realized there was a connection when she observed both strains had prehensile tails, rather like monkeys. Vonda McIntyre introduced her own feline species in the first publish Pocket Books Trek novel, "The Entropy Effect". Lt. "Snarl" (a nickname never mentioned within her range of hearing) had spots like a leopard and ruby colored fangs. She also tended to go on all fours when flat out running. She served on security detail and few were foolish enough to try fighting her.
M'Ress's hands in the first (and perhaps the last) pictures in this thread (so far) look the most believably cat-like. The human-like hands in the others don't really work for me, especially in contrast to her feline feet.
Well, graphite drawings naturally allows one greater control of the details. The figure in the 3D renderings is derived from an Anime/Manga inspired mesh called Aiko 3, available at the www.daz3d.com
on-line store. A third-party vendor created an "add-on" package that reshapes the geometry of the shins, feet and toes to create an anthropomorphic styled character. The vendor did not provide any features that would morph Aiko's delicate human fingers into thicker, stubbier paw-like digits. I freely admit I am not an organic modeler. I had to make do with what I had.
I'd also like to see more of her tail (that sounded wrong -- or did it? ) I'm curious to see how the feline tail joins the more human-looking derriere.
In short, it doesn't. The tail is a separate "conforming figure" that is "parented" to the hip region. If I were to depict a scene with M'Ress "in the fur" using the 3D model, I'd have to "cheat" by using "post-work" to blend the tail with the hip. Wearing her uniform, the tail simply extends below her skirt. The Bros. Grinn of the web-comic "SuperMegatopia" did realize an occupational hazard for M'ress while wearing the "classic" mini-skirt uniform. What happens should the poor kit' raise her tail? This: