The American journal of anatomy . These relations are indicated in adiagram (Fig. 11). After the stage at which the partial connection between hypophysisand archenteron is seen, there is a further bending of the brain, theflexure becoming excessive in amphibians. The bending, togetherwith the expansion of the forebrain, results in pushing the hypophysis .1. II. Johnston. and preoral entodi rm farther and farther back, until they cometo lie close to the end of the notochord. Compare Figs. 3 and is this movement of the preoral entoderm dorso-caudally that wasreferred to above as the means o
The American journal of anatomy . These relations are indicated in adiagram (Fig. 11). After the stage at which the partial connection between hypophysisand archenteron is seen, there is a further bending of the brain, theflexure becoming excessive in amphibians. The bending, togetherwith the expansion of the forebrain, results in pushing the hypophysis .1. II. Johnston. and preoral entodi rm farther and farther back, until they cometo lie close to the end of the notochord. Compare Figs. 3 and is this movement of the preoral entoderm dorso-caudally that wasreferred to above as the means of thickening up the wall of the archen-teron which is Left so thin by the splitting off of the head mesen-chyme. The hypophysis finally comes to lie on the dorsal surfaceof the preoral entoderm, and the notch which represents the originalpreoral cavity is visible up to the stage when the velum transversum,epiphysis, paraphysis and the inferior lobes of the brain are allwell formed (Fig. 10). The formation of the saccus vasculosus. Fig. 10. A. punctatuin, stage after formation of epiphysis. Median sagittalBection. The palseostomal recess is a deep angular pit. The dental ridgesare growing in. Haemalum. and the differentiation of other structures in the region of the inferiorLobes takes place considerably later. The shifting caudad of the preoral entoderm and hypophysis whichI have attributed to the brain flexure is accompanied by a very con-siderable elongation of the mouth entoderm. While the shifting isInking place the mouth entoderm is compressed into a solid mass,and this becomes elongated into a comparatively slender cord, flat-tened dorso-ventrally (Figs. 10, 12, 14, 16). For some time after its separation from the ectoderm the hypophy-sis continues to have the form of a shallow cup with the convexity The Limit Between Ectoderm and Entoderm. 53 against the brain, the concavity toward the entoderm (Fig. 9). Itfinally forms a somewhat ovoid mass and lies beneath the
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectanatomy, bookyear1910
