. The elasmobranch fishes . A B Fig. 50a. The median branchial cartilages, Heptanchus maculatus, dorsal view. (H. M. Gilkej, del.) Fig. 50b. Area of rudimentary arches, Heptanchus maculatus, ventral view. ;, ninth arch; hb.', second basibranchial; hh., basihyoid; ch., ceratobranehial; ch., ceratohyoid; hh., hypobranchial; mp., median piece; r., rudimentary rays; x., part of eighth arch. In the midventral line of the branchial basket is a series of unpaired pieces which unite the arches of opposite sides. The first of these is the basihyoid pre- viously mentioned (hh., fig. 50a). A fir
. The elasmobranch fishes . A B Fig. 50a. The median branchial cartilages, Heptanchus maculatus, dorsal view. (H. M. Gilkej, del.) Fig. 50b. Area of rudimentary arches, Heptanchus maculatus, ventral view. ;, ninth arch; hb.', second basibranchial; hh., basihyoid; ch., ceratobranehial; ch., ceratohyoid; hh., hypobranchial; mp., median piece; r., rudimentary rays; x., part of eighth arch. In the midventral line of the branchial basket is a series of unpaired pieces which unite the arches of opposite sides. The first of these is the basihyoid pre- viously mentioned (hh., fig. 50a). A first basibranchial piece is lacking, but basibranchials are present on the second to the fourth arches following (hh-''^). A large median piece posteriorly {mp.) serves for the attachment of the fifth and sixth hypobranchials and the seventh ceratobranehial (cbJ). All these arches, except the last, have cartilaginous branchial raj's on their epi- and ceratobranehial segments. These branchial rays, though simpler than those on the hyoid arch {, figs. 48 and 49), serve the same function of sup- porting the gill septa. The visceral arches are further provided with superficially placed pieces, the extravisceral cartilages. Those accompanying the first or mandibular arch
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