. On the anatomy of vertebrates. Vertebrates; Anatomy, Comparative; 1866. 0-20 ANATOMY OF VERTEBRATES. 428 largest at one end, and impressed by a slight longitudinal fissure. The rudiments of the neural axis are first recognisable in the two parallel longitudinal elevations (' primitive trace' or ' laminaj dorsales,' ib. m, n) bordering the fissure. Beneath these is at the same time forming the notochordal rudiment of the vertebral column, ib. c. The albuminous principle is concentrated in m, the gelatinous one in c: this chemical differentiation does not aifect n. The polyhedral cells extend
. On the anatomy of vertebrates. Vertebrates; Anatomy, Comparative; 1866. 0-20 ANATOMY OF VERTEBRATES. 428 largest at one end, and impressed by a slight longitudinal fissure. The rudiments of the neural axis are first recognisable in the two parallel longitudinal elevations (' primitive trace' or ' laminaj dorsales,' ib. m, n) bordering the fissure. Beneath these is at the same time forming the notochordal rudiment of the vertebral column, ib. c. The albuminous principle is concentrated in m, the gelatinous one in c: this chemical differentiation does not aifect n. The polyhedral cells extend the vertebral layer on each side of the ' primitive trace,' which also increases in length: the neural columns, at first flat and horizontal, rise at their outer margins, approximate, and ultimately unite aljove, where they are covered by the peripheral cell-layer, a: they are also defended by the nascent ncurapophyses, ib. n. Meanwhile the ' animal' layer is extending laterally, ib. h, beneath the investing membrane, a; and tlie cephalic end of the embryo enlarges and raises itself from the yolk-bed. A section of the ovum just jirior to the coalescence of the ' lamina} dorsales ' to form the neural axis, as in fig. 428, shows, a, the dark investing membrane, or ' cambium :' b, the museulo-tegumentary layer, inclosing the whole yolk, v ; m, the myelonal columns ; c, the notochord ; n, the blastema, in which cai'tilaginous rudiments of the ncurapophyses begin; /(, the cavity, beneath the germ due to solution of the yolk-sul)stance. On the ventral aspect of the embryo lavers of cells have been forming two parallel ridges projecting into the yolk ; and the intermediate space is converted by liquefaction of cells into a primitive alimentary groove. But all the systems and organs for the support of the cmliryo begin to be developed after the main basis of tlie neural and vertebral parts has been establislicd. Figure 429, a, gives a view of the embryo of the Frog from the dorsal aspe
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Keywords: ., bookauthorowenrichard18041892, bookcentury1800, bookdecade1860
