. The Journal of comparative neurology and psychology. tin embryos between 6 mm. and 9 mm., but is always clearly present in9 mm. embryos (Fig. 36). After this time the sac grows out andenwraps the tip of the hypophysis and the relations familiar to allembryologists are established. The outgrowth of this sac is the ear-liest mark of the position of the infundibulum and this is a consid-erable distance behind the primitive optic groove, as in selachiansand amphibians. In later development the floor of the primitive Johnston, Forchrain Vesicle in Vertebrates. 499 inferior lobe becomes dra^vni do
. The Journal of comparative neurology and psychology. tin embryos between 6 mm. and 9 mm., but is always clearly present in9 mm. embryos (Fig. 36). After this time the sac grows out andenwraps the tip of the hypophysis and the relations familiar to allembryologists are established. The outgrowth of this sac is the ear-liest mark of the position of the infundibulum and this is a consid-erable distance behind the primitive optic groove, as in selachiansand amphibians. In later development the floor of the primitive Johnston, Forchrain Vesicle in Vertebrates. 499 inferior lobe becomes dra^vni down in funnel shape and the lateralportions become thickened as the tuber cinereum. It is one of thepeculiarities of the mammalian and human brain that the infun-dibulum is drawn doM-n close behind the chiasma and forms a deeperand narrower funnel than in lower vertebrates. There is no funda-mental difference of relations. The evidence that the fold in the roof which has been called thev^elum transversum is correctly identified may be seen in Figs. 34. Fig. 37. Pig embrjo, 12 iiuii. Mediau .sagittal section, reconstructed fromseveral sections, x 15. to 39. The posterior commissure is a point about which there is nodispute. In the arch (neuromere) in front of it appears later theepiphysis (Fig. 38). In front of the epiphysis and in the same archappears the commissura hahenularis. This arch then is the roof ofthe diencephalon. It is bounded in front in all other classes ofvertebrates by the velum transversum. The fold to which this namehas been given lies in the proper segmental position. This is furthersupported by its relations to the structures in front of it. Immedi-ately in front of the velum the roof is raised in a distinct arch. 500 Journal of Comparative Neurology and Psychology. This corresponds in position to the paraphysis of lower forms ( 30 to 33). Since there is no glandular development knownin mammals, it may be called the paraphysal arch, a name whichMinot
Size: 1751px × 1427px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthorwistarinstituteofanat, bookcentury1900, bookdecade1900
