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Re: choana [was SOME SVP TIDBITS]



Norm King wrote (10/9/98; 9:08a):

>Some clarification, please, for us non-anatomists:<

>Tom Holtz said (10/9/98; 9:41a):<


>>>Perhaps someone could say what a choana is too?<<<

>>Sorry, let that one slip out. Internal nostril (the opening inside 
the roof of the mouth at the other end of the nasal passage).  In 
mammals and our ancestors, birds, and modern crocs it is far back in 
the throat; in most
other reptiles (including non-maniraptoriform, and non-spinosaurid,
theropods) it opens closer to the front of the mouth.<<


>First:  I always use the term internal naris for the opening through 
bone, and thought "nostril" implies inclusion of associated soft tissues 
(analogous to orbit vs. eye socket).<

>Second:  Is "choana" really synonymous with "internal naris", or does it 

refer to the opening where inhaled air passes freely into the opening of 
the mouth cavity or throat (implied above).  In other words, for animals 
that have a secondary palate, is the choana farther back than the 
internal naris?  This implies to me that choana and internal naris are 
different.  Might internal naris still be the proper term for the more 
anterior opening, but one that opens into a passage between the primary 
and secondary palate (leading ultimately to a more posterior opening 
where the air hits the freer space of mouth cavity and/or throat, that 
perhaps has a different name???)?<

>Thanks, in advance.<

Since no one felt inspired to jump on this one, I must answer it myself.  


I had to ask several people, some of whom know a bit of anatomy and are 
involved in our premed and predental programs.  They generally never 
heard the term.  Our resident herpetologist and chordate phylogenist (is 
that a word?) finally came to the rescue.  It turns out there are two 
definitions.

One is that the choana is the passageway by which animals get air into 
the mouth/throat while keeping the mouth closed.  It appeared first among 
sarcopterygians, and sarcopertygians plus tetrapods are "choanates".  It 
includes everything from the external nostrils to the internal nostrils 
(nares, if we're just talking about holes through the bone), or from the 
external nostrils to the back of a secondary palate, for animals that 
have one.  It is the whole passageway; there is no special name for the 
passage between the primary and secondary palate.

As you can see, this is not quite synonymous with internal nostril 
(naris).  

The other definition is that it is the same thing as internal nostril.  
Of course, if you have a choana, then you also have an internal nostril, 
and vice versa.

I suspect that the first definition was the original one.  Otherwise, why 
have a separate word?  Then, through use (misuse?), it came to also mean 
internal nostril.  I'm speculating.


Anyway, now I feel better.  Thank you, Norm.

You're welcome, Norm.


*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*
Norman R. King                                       tel:  (812) 464-1794
Department of Geosciences                            fax:  (812) 464-1960
University of Southern Indiana
8600 University Blvd.
Evansville, IN 47712                      e-mail:  nking.ucs@smtp.usi.edu






*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*
Norman R. King                                       tel:  (812) 464-1794
Department of Geosciences                            fax:  (812) 464-1960
University of Southern Indiana
8600 University Blvd.
Evansville, IN 47712                      e-mail:  nking.ucs@smtp.usi.edu