Dictionary of Ichthyology  

Meckel's cartilage = the functional lower jaw of Elasmobranchii and Holocephali, the embryonic lower jaw of other gnathostomous vertebrates which ossifies at least in part as the mentomeckelian, mediomeckelian, coronomeckelian, articular and retroarticular. It remains in some adult fishes as a pointed rod embedded in the dentary and angular. Also called mandibular cartilage, ceratomandibular cartilage or primary mandible. See also Bridge's ossicles.

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