. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. In the spiny dogfish (Fig. 231) as well as most other elasmobranch fishes, the second or hyoid arch, emancipated like the mandibular arch from bearing gills, serves as a support for the primary tongue and also as a suspensory apparatus, furnish- ing the only points of articulation between the neur- ocranium and the splanchnocranium. The tongue support includes a median basihyal which runs across the anterior part of the tongue and to each end of which is a
. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. In the spiny dogfish (Fig. 231) as well as most other elasmobranch fishes, the second or hyoid arch, emancipated like the mandibular arch from bearing gills, serves as a support for the primary tongue and also as a suspensory apparatus, furnish- ing the only points of articulation between the neur- ocranium and the splanchnocranium. The tongue support includes a median basihyal which runs across the anterior part of the tongue and to each end of which is attached a ceratohyal. From the posterior, or embryonic dorsal, end of each cera- tohyal, a hyomandibular runs medially to attach to the side of the otic region of the neurocranium. The posterior end of the upper jaw is attached at the junction of hyoman- dibular and ceratohyal. The five posterior arches are gill arches that, somewhat in the manner of ribs, extend protectively around the anterior end of the digestive tube (Fig. 479). Between these pairs of arches are gill slits, which allow water Fig. 478. Diagram to show how the primitive upper and lower jaws form from a horseshoe- shaped cartilaginous *vC~ Medulla Oblongata /&''%-':')< V W "%-Ear Tâ77r~ Neurocranium /1'{ w^- -ss^3*i '.ââ /- -|jâNotochord ~£ \râ Pharyngobranchial imUiUu4w%. ;T"~Epibranchial â Pharynx /4-T7 Ceratobranchial f ''/ _ .i'i Hypobranchial "''^:zzt^z-"z'''' Basibranchial Fig. 479. Cross section diagram of primordial neurocranium and splanchnocranium. entering the mouth to pass out on either side after bathing the vascular gills that hang suspended from the arches. The gill arches diminish in size pos- teriorly and in numbers in bony fishes, the loss always coming at the pos- terior end of the series. In a few of the more primitive elasmobranchs there are present six and even seven pairs of gill arches, but the usual number is five. In higher vertebrates only t
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