The Collaborative International Dictionary of English v.0.48:

Epibranchial \Ep`i*bran"chi*al\, a. [Pref. epi- + branchial.]
   (Anat.)
   Pertaining to the segment between the ceratobranchial and
   pharyngobranchial in a branchial arch. -- n. An epibranchial
   cartilage or bone.
   [1913 Webster]