Outlines of comparative physiology touching the structure and development of the races of animals, living and extinct : for the use of schools and colleges . i-cate the first for-mation of theeyes; it is thecell of the thala-mi and crura ofthe cerebrum ;the second small-er cell (d2) is thecell of the cor-pora quadrigemi-na ; the third, anelongated cell(</3), belongs tothe medulla ob-longata. Thetransparent massof the brain andspinal cord ac-quires greaterconsistency, and is covered with af ijr. 333.—Yolk of the natural size after thirty- fi , , . , , six hours of incubation ; a, yolk ; b, f
Outlines of comparative physiology touching the structure and development of the races of animals, living and extinct : for the use of schools and colleges . i-cate the first for-mation of theeyes; it is thecell of the thala-mi and crura ofthe cerebrum ;the second small-er cell (d2) is thecell of the cor-pora quadrigemi-na ; the third, anelongated cell(</3), belongs tothe medulla ob-longata. Thetransparent massof the brain andspinal cord ac-quires greaterconsistency, and is covered with af ijr. 333.—Yolk of the natural size after thirty- fi , , . , , six hours of incubation ; a, yolk ; b, fiddle-shaped I ellucid area, in the middle of which the embryo transparent lay-is seen. In the vascular area, c, c, the insulae er, the futuresanguinis, or blood islets, begin to appear. membranous ill- Fig. 332.—Ideal sections of fig. 331.—A,transverse section ; B, longitudinal section. InA,/, section of the vertebral laminae. In B,formation of the head by the reflection of theblastoderma ; e, margin of the involucrum capitis,and entrance into the,future intestinal canal (foveacardiaca of Wolff). The other references are thesame as in fig. DEVELOPMENT OF THE CHICK—3TIKST PERIOD. 303 volucra of the nervous centres ; the brain, and medulla ob-longata, up to thistime, are, therefore,in fact, shut vesicles,which, on account oftheir transparencyonly, appear as openspaces lying betweenthe sinuous cristse ofthe dorsal , from thecristae of the dorsallaminae, and the four-cornered laminae ofthe vertebral arches,proceeds the serouslamina of the germi-nal membrane, thick-ening as it grows,and bending fromboth sides at thesame time slightlyinwards ; in this parta number of smalldark leaflets maketheir appearance si-multaneously, whichbecome particularlyplain in the trans-verse section (, A, and especi-ally fig. 338, A, b2)-these are the rudi-ments of the trans-verse processes ofthe vertebrae, and,farther out, of the Fig. 334.—Magnified view of the a
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectzoology, bookyear1870
