The elasmobranch fishes elasmobranchfish03dani Year: 1934 48 THE ELASMOBRANCH FISHES intercalary piece (id.). Both of these cartilages are more or less triangular in shape, the former having its base on the centrum, the latter with apex pointing toward the centrum. Above the dorsal plate there may be pieces segmented off () to form the so-called neural spines, and in the most anterior part of the column two such pieces may be present one above the other (fig. 47). Each dorsal plate in the anterior region is further perforated by a ventral root () of the spinal nerve, and each dorsal
The elasmobranch fishes elasmobranchfish03dani Year: 1934 48 THE ELASMOBRANCH FISHES intercalary piece (id.). Both of these cartilages are more or less triangular in shape, the former having its base on the centrum, the latter with apex pointing toward the centrum. Above the dorsal plate there may be pieces segmented off () to form the so-called neural spines, and in the most anterior part of the column two such pieces may be present one above the other (fig. 47). Each dorsal plate in the anterior region is further perforated by a ventral root () of the spinal nerve, and each dorsal intercalary by the dorsal root () of the same nerve. In this region and ventral to the central column are also ventral plates (bv., fig. 51). On the third and succeeding vertebrae back to the forty-fifth, ribs (r.) are present. The eighth to twenty-fourth ribs in Hepfanclius, like some of those in Laemargus (Helbing, 1904, cited on p. 72), are divided into Fig. 53. Lateral view of spinal column in transitional area. Drawai as transparent object. (Katharine Rogers, orig.) (For explanation see fig. 52.) an anterior and a posterior part, the former of which is a curious plate-like process projecting forward and downward. Between two ventral plates there is interpolated a small ventral intercalary piece (iv.). A sagittal section through this region (fig. 52) shows the central column composed of three concentric layers in the notochordal sheath. These layers surround the notochord (chd.) and constrict it at intervals into a bead-like chain. The outermost of these layers is relatively thin and consists of carti- lage; within this cartilage is a second and lighter broad area (, fig. 52) which appears to be made up of transverse fibers. Within this second layer and bounding the notochord is a third layer (is.) of a white tissue. At regular intervals the third layer forms septa (s.) which produce the regular constric- tions in the central part of the notochord. It w
Size: 3213px × 623px
Photo credit: © Bookend / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: archive, book, drawing, historical, history, illustration, image, page, picture, print, reference, vintage
