Sentence:  Inside of this area it is possible to identify clearly two parallel echonegative zones, which belong to the nasal cavities (<WSD>choanas</WSD>) and are placed on both sides of a medial structure, considerably echogenic, which corresponds to nasal bridge (Fig. 2.12.) 
Meaning of the word marked with <WSD> tags:  An opening towards the back of the nasal cavity; the posterior nasal aperture.