. The science and art of midwifery. Fig. 5t>.—Development of spinal cord and brain of human subject (Longet). A, brain andspinal cord at seventh week. B, more advanced stage ; &, spinal cord ; a, enlargement ofthe spinal cord with its anterior curvature ; c, cerebellum; e, tubercula quadrigemina;/, optic thalamus; g, cerebral hemispheres. C, brain and spinal cord at eleventh week,as in foregoing ; o, optic nerve of the left side. C, vertical section of the preceding. Lumbar and brachial enlargements likewise form at the points atwhich the nerves are given off to the upper and lower extremit
. The science and art of midwifery. Fig. 5t>.—Development of spinal cord and brain of human subject (Longet). A, brain andspinal cord at seventh week. B, more advanced stage ; &, spinal cord ; a, enlargement ofthe spinal cord with its anterior curvature ; c, cerebellum; e, tubercula quadrigemina;/, optic thalamus; g, cerebral hemispheres. C, brain and spinal cord at eleventh week,as in foregoing ; o, optic nerve of the left side. C, vertical section of the preceding. Lumbar and brachial enlargements likewise form at the points atwhich the nerves are given off to the upper and lower extremities. In the very earliest stages of development, there appears, just be-neath the primitive groove, a cylindrical body, tapering at both extrem-. 61 PHYSIOLOGY OF THE OVUM. ities, of a cartilage-like consistence, and extending the entire lengthof the embryo. This organ is termed the chorda dorsalis (ch., ). It is a temporary structure, but of great interest from its sus-taining an intimate relation in the vertebrate classes to the produc-tion of the bony skeleton. Upon either side of the chorda dorsalis, and running parallel to it,two longitudinal masses (vide Fig. 57) are separated off from the cen-tral portions of the intermediatelayer. They are sometimes termedthe primitive vertebral plates,though they are more properlycolumns. They are concernedin the formation of the verte- i ~ +i ~ ~.„~^?^ ~* i\*~ v i Fig. 57.—Diagram representing transverse sec-brae, the muscles Of the back, tion through the embryo of a chick at the and the origin of the spinal «nd f *ne ^Tst7 d^ °f incubation, m, ° • -i -i dorsal plates; c/i, chorda aorsahs; v, ver- nerves. The two peripheral por- tebrai chords; ap, abdominal plates. tion
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Keywords: ., bookcentury1800, bookdecade1890, bookidsci, booksubjectobstetrics
