Elements of the comparative anatomy Elements of the comparative anatomy of vertebrates elementsofcompar00wied Year: 1886 FIG. 21.—PORTION OF THE VERTEBRAL COLUMN OF Spatularia. (Side view.) FIG. —TRANSVERSE SECTION OF THE VERTEBRAL COLUMN OF Acipcnser ndlienus (iu the anterior part of the body). P;(, spinous process ; EL, longitudinal elastic band ; SS, skeletogenous layer ; Ob, upper arch; M, spinal cord; P, pia mater; Ic, intercalary pieces; Cs, noto- chorJal sheath ; 0, notochord ; Ee, elastica externa ; Ul>, lower arch ; Ao, aorta ; Fo, median parts of the lower arches, which enclo
Elements of the comparative anatomy Elements of the comparative anatomy of vertebrates elementsofcompar00wied Year: 1886 FIG. 21.—PORTION OF THE VERTEBRAL COLUMN OF Spatularia. (Side view.) FIG. —TRANSVERSE SECTION OF THE VERTEBRAL COLUMN OF Acipcnser ndlienus (iu the anterior part of the body). P;(, spinous process ; EL, longitudinal elastic band ; SS, skeletogenous layer ; Ob, upper arch; M, spinal cord; P, pia mater; Ic, intercalary pieces; Cs, noto- chorJal sheath ; 0, notochord ; Ee, elastica externa ; Ul>, lower arch ; Ao, aorta ; Fo, median parts of the lower arches, which enclose the aorta ventrally ; Z, basal processes of the lower arches. The strong, concentrically-layered notochordal sheath (Fig. 22, Cs) here plays the part of vertebras, and is surrounded by a fibrous skeletogenous layer (Fig. 22, S3), in which paired dorsal and ventral cartilages become developed. The former give rise to the above-mentioned upper or neural arches, the latter to the lower or hsemal arches (Figs. 21,22, Ob, Ufy. In the caudal region C FIG. 23.—PORTION OF THE VERTEBRAL COLUMN OF Protoptcrus. (Side view.) C, notochord ; DF, spinous process ; FT, interspinous bone ; FS, fin-ray. the latter enclose the aorta and caudal vein; further forwards the cartilages do not meet in the middle line below, and consequently the lower arches end on either side in a laterally-directed cartila- ginous projection, or 'basal process,' which may develop an D 2
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