PHYLUM CHORDATA 



413 



union of a pair of frontals in front with a pair of parietals 

 behind. Over the olfactory capsules are a pair of triangular 

 nasals (NA), and applied to their ventral surfaces small 



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paired vomers (VO). On the ventral surface of the skull 

 is a large T-shaped parasphenoid {PA. SPH), its stem 

 underlying the base of the cranium, while its two arms ex- 

 tend outwards beneath the auditory capsules. 



