The development of the human body; a manual of human embryology . r cavities communicate with thethird ventricle, the foramina of Monro, being relativelyvery large (Fig. 224), but, in later stages (Fig. 217), theyincrease more markedly and eventually surpass all theother portions of the brain in magnitude, overlapping andcompletely concealing the roof and sides of the dienceph-alon and mesencephalon and also the anterior surfaceof the cerebellum. In this enlargement, however, theforamina of Monro share only to a slight extent, and con-sequently become relatively smaller (Fig. 217), formingin t
The development of the human body; a manual of human embryology . r cavities communicate with thethird ventricle, the foramina of Monro, being relativelyvery large (Fig. 224), but, in later stages (Fig. 217), theyincrease more markedly and eventually surpass all theother portions of the brain in magnitude, overlapping andcompletely concealing the roof and sides of the dienceph-alon and mesencephalon and also the anterior surfaceof the cerebellum. In this enlargement, however, theforamina of Monro share only to a slight extent, and con-sequently become relatively smaller (Fig. 217), formingin the adult merely slit-like openings lying between thelamina terminalis and the optic thalami and having fortheir roof the anterior portion of the velum interpositum. The velum interpositum,—that is to say, the roof-plate,—-where it forms the roof of the foramen of Monro, isprolonged out upon the dorsal surface of each hemisphere,and, becoming invaginated, forms upon it a groove. Asthe hemispheres, increasing in height, develop a mesial THE TELENCEPHALON. 421. wall, the groove, which is the so-called chorioidal fissure,comes to lie along the ventral edge of this wall, and as thegrowth of the hemispheres continues it becomes more andmore elongated, being carried at first backward (Fig. 225),then ventrally, and finally forward to end at the tip ofthe temporal lobe. After the establishment of the groovesthe mesenchyme in their vicinity dips into them, and,developing blood-vessels, becomes the chorioid plexusesof the lateral ventricles, and at first these plexuses growmuch more rapidly than theventricles, and so fill them al-most completely. Later, how-ever, the walls of the hemi-spheres gain the ascendancy inrapidity of growth and theplexuses become relatively muchsmaller. Since the portions ofthe roof-plate which form thechorioidal fissures are continu-ous with the velum interpositumin the roofs of the foramina ofMonro, the chorioid plexuses ofthe lateral and third ventriclesbe
Size: 1884px × 1326px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, booksubjectembryol, bookyear1902
