. The comparative anatomy of the domesticated animals. Veterinary anatomy. TEE FCETUS. Article II.âDevelopment of the Various Organs in the Animal Economy. Development of the Nervous System. We will at first glance at the development of the nervous centresâthe Irain and spinal cord ,â then their peripheral partsâthe tierves. 1. First differentiations of the neuraxis.âThe trace of the central nervous system or neuraxis, resides, or has been seen, in the primitive groove, resulting from an inflection of the thickened ectoderm (Fig. 551). The complete invagina- tion of the ectoderm brings about t
. The comparative anatomy of the domesticated animals. Veterinary anatomy. TEE FCETUS. Article II.âDevelopment of the Various Organs in the Animal Economy. Development of the Nervous System. We will at first glance at the development of the nervous centresâthe Irain and spinal cord ,â then their peripheral partsâthe tierves. 1. First differentiations of the neuraxis.âThe trace of the central nervous system or neuraxis, resides, or has been seen, in the primitive groove, resulting from an inflection of the thickened ectoderm (Fig. 551). The complete invagina- tion of the ectoderm brings about the formation of a tubeâthe neural canal (Fig. 552). From the thirty-sixth hour, the medullary laminae are close to each other in front in the middle line, but are not yet fused together. From Fig. TRANSVERSE SECTION OF THE BODY OF AN EMBRYONIC DUCK, THREE DAYS OLD. (AFTER BALFOUR.) om., Amnion; so., somatopleure; sp., splanchnopleure ; wd, Wolffian canal; st, segmentary tube ; ,, cardinal vein ; , muscular lamina, or plate; , spinal ganglion; , spinal cord; ch., notochord ; ao., aorta ; hy, endoderm. the fortieth hour, the neural canal is closed as far as the rhomloidal sinusâthe lozenge-shaped space where the primitive groove is widest. Towards its anterior part, the neural canal shows three successive dilatations âtracts of the brain, and constituting the three primitive cerebral vesicles. The remainder of the neural canal forms the spinal cord. 2. Development of the brain.âThe cerebral vesiclesâat first three in number, and distinguished as anterior, middle, and posteriorâsoon undergo an increase to five. The anterior cerebral vesicle throws out two hollow prolongations which become the cerebral hemispheres, and now constitute the anterior brain. On the other hand, the anterior cerebral vesicle itself becomes the vesicle of the optic thalami, or intermediate brain (see Fig. 568).. Please note that these images are extracted from scanned page
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