Cartilaginous ring

Osteichthyes (), popularly referred to as the bony fish, is a diverse taxonomic group of fish that have skeletons primarily composed of bone tissue. They can be contrasted with the Chondrichthyes, which have skeletons primarily composed of cartilage. [Source: Wikipedia ]

Synonyms
Tracheobronchial rest
May Cause
Localized narrowing of esophagus