Generally, the number and position of limbs should match. Beyond that it's up to the DM.
Disguise Self has similar wording:
You can seem 1 foot shorter or taller and can appear thin, fat, or in between. You can’t change your body type, so you must adopt a form that has the same basic arrangement of limbs. Otherwise, the extent of the illusion is up to you.
But there are no strict rules about what "body type" means.
We can assume that shapes with a different number of limbs -- a centaur or a xorn or a marilith demon -- are definitely not possible. And presumably (assuming humanoid targets) both seeming and disguise self can produce the forms of other humanoids.
But there are a few other cases that might obtain, and it's up to the DM to rule in these cases:
Quadrupeds. Animals like wolves (as mentioned in the question) have limbs with the same number of joints at the same general positions on the torso. So an argument could be made that they have the same "basic arrangement of limbs" as a humanoid. Contrariwise, an argument could be made that arms are not the same as legs, or that plantigrade legs (like humans and bears have) aren't the same as digitigrade legs (like a canine or feline has). This is really a DM call; the intent of disguise self seems to be that such forms are not ones the spell can produce; with seeming it's not so clear.
Tails. Are tails limbs? Can a tiefling hide their tail with disguise self or seeming? Can a humanoid without a tail use seeming to appear like a lizardfolk, with a substantial tail? Here we have a Sage Advice rulings:
A tiefling's tail isn't considered a limb; it's not prehensile.
From this we can assume that limbs that don't have any game effect aren't considered for this purpose.
If I were DM in this case, I would rule that seeming (and disguse self) can't cause humans to appear as quadrupeds, and that those spells can't hide (or produce) a tail that functions as more than a cosmetic detail.