Dictionary of Ichthyology  

gill arch = the endochondral skeletal support of the gill which bears the gill filaments and the gill rakers. Consists of pharyngobranchials, epibranchials, ceratobranchials and hypobranchials. Usually 4 in teleosts, can be as many as 16 in some Cyclostomata.

Shark skull, a = auditory capsule, b = basibranchial, c = keratobranchial, e = epibranchial, g = gill cleft, h = hyoid, hm = hyomandibula, l = labial cartilages, m = mandible (Meckel's cartilage), o = olfactory capsule, p = pharyngobranchial, pq = pterygoquadrate, r = rostrum, s = spiracle, 2, 5 = exits of second and fifth nerves, I-V = branchial arches., from Kingsley's "Textbook of Vertebrate Zoology, 1906. Photograph by Brian W. Coad.

Canadian Museum of Nature