Everyone has that small linguistic pet peeve. For some, it’s the differentiation between well and good. For others, it’s the improper use of apostrophes. For me, it’s improper plurals in scientific jargon.
When most English speakers need to make a word plural, the first instinct is to just add an ‘s’ to the end; if one is femur, then two must be femurs. Nope. Of all of these linguistic sins, in my experience this one is the most common. To make the word ‘femur’ plural, you add an ‘a’ instead of an ‘s’ (and tweak the spelling a bit); one is a femur and two are femora. Besides, femora is just more fun to say!
Let’s stick with the osteological focus. Again, for most people their first instinct is to turn ‘radius’ into ‘radiuses’ in order to make it plural. Instead, take off the ‘us’ and add an ‘i’; one is a radius, two are radii. Radii is one of my favorite plural words and it’s just so much fun to say!
And the last osteological term: scapula. And again, don’t add an ‘s’, just add an ‘e’. That probably seems counterintuitive but one is a scapula and two are scapulae.
Genus is a tough one. Some people default to trying to simply add an ‘s’ but others seem to know thats not right and try something else. Others don’t change the word at all in order to make it plural. I’ve heard many variations but the most common are ‘genuses’ and ‘genii’. Genus doesn’t act like the other words in this list; the plural form of ‘genus’ is ‘genera’. So that’s it.
Femur -> Femora, Radius -> Radii, Scapula -> Scapulae, Genus -> Genera.
And if this is confusing, just do what I do: use a different word! I tell my students that synonyms are for when you can’t spell or pronounce the word that you actually want to use. But really, don’t let this scare you. When in doubt, just power through and act confident even if you don’t feel it.