extrabranchial

Century Dictionary and Cyclopedia

1. Lying outside of or external to the branchial arches; forming the external support of the branchial septa.
2. n. A term applied by W. K. Parker to certain cartilages which take part in the formation of supports for the divisions between the gill-chambers in tadpoles, lampreys, and sharks. In lampreys the extrabranchials are the vertical bars of the branchial basket; in sharks they are the cartilaginous bands external to the rays of the branchial septa.

Wiktionary

1. adj. anatomy Outside of the branchial arches.

GNU Webster's 1913

1. adj. (Anat.) Outside of the branchial arches; -- said of the cartilages thus placed in some fishes.