Isn't everyone being a bit tough on McCoy?
Aren't there like 100s of different species in the Federation?
I'd expect him to concentrate on knowing their anatomy before that of an enemy.
He's only human. I'd expect the EMH to know it and Bashir but Crusher and McCoy not to be an expert on everything. Crusher should know it because she's got a Klingon as crew.
Even your local vet would not be able to say fix an elephant without consulting an expert or looking up some books. Its not something he or she is ever likely to encounter in a general practice.
Its ridiculous that McCoy doesn't know much about Vulcan physiology though but thats probably got a lot to do with Vulcan's being so secretive about things.
I'm a computer programmer but it would be like sending me a job and telling me to fix a computer that I had no experience in. I can't know every computer system and language in the world. Thats why I laugh to myself when Spock or Scott or Geordi come across alien technology and are experts in it straight away