. The elasmobranch fishes . Fig. 51 Fig. 51. Fifth to eighth segments of the spinal column, Heptanchus maculatus. Fig. 52. Sagittal section through sixth to eighth segments of the column. (, del.) bd., dorsal basal (basidorsal) plate; bv., ventral basal (basiventral) plate; c, central column; chd., unconstrieted part of notochord; , foramen for dorsal root nerve; , foramen for ventral root nerve; , haemal arch; id., dorsal intercalary (interdorsal) plate; iv., ventral intercalary piece; is., layer immediately around the gelatinous notochord; , middle layer in s
. The elasmobranch fishes . Fig. 51 Fig. 51. Fifth to eighth segments of the spinal column, Heptanchus maculatus. Fig. 52. Sagittal section through sixth to eighth segments of the column. (, del.) bd., dorsal basal (basidorsal) plate; bv., ventral basal (basiventral) plate; c, central column; chd., unconstrieted part of notochord; , foramen for dorsal root nerve; , foramen for ventral root nerve; , haemal arch; id., dorsal intercalary (interdorsal) plate; iv., ventral intercalary piece; is., layer immediately around the gelatinous notochord; , middle layer in sheath of notochord; , neural canal; oz., cartilage; r., rib; s., sep- tum constricting notochord ; , so-called neural spine. branchial arches. An eighth appears directly back of the last functional arch (ch.^, fig. 50a) and even a ninth arch may be indicated nearer the middle line (ar.^, fig. 50b), (Daniel, 1916). Spinal Column The spinal column in Heptanchus, because of its simplicity, is especially inter- esting. Unlike that of the higher Elasmobranchs, it consists of a long central column {c, fig. 51) which is essentially the enlarged sheath of the notochord. Anteriorly the column is more or less continuous with the occipital region of the cranium (see fig. 47) and posteriorly it extends to the tip of the tail. Above this central cohunn there is a series of neural arches formed for the protection of the spinal cord; below it, in the region of the tail, is a similar series of haemal arches {, fig. 53) for the protection of the caudal artery and vein. A segment of the column in the so-called neck region shows the central part well developed. Above this central part are the neural plates making up the neural arch. Each arch is composed of a dorsal plate (hd., fig. 51) and a dorsal
Size: 2752px × 1816px
Photo credit: © The Bookworm Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookpublisherberkeleycalifuniversityofcaliforn
