The development of the human body; a manual of human embryology . groove, while each lateralwall is divided into a dorsal and ventral zone by a grooveknown as the sulcus Monroi(Sm), which extends forwardand ventrally toward thepoint of origin of the opticevagination (Fig. 224). Atthe posterior end of the ridge-like elevation which repre-sents the roof-plate is arounded elevation (Fig. 223,p) which, in later stages,elongates until it almostreaches the dermis, forminga hollow evagination of thebrain roof known as thepineal process. The distalextremity of this process en-larges to a sac-like stru
The development of the human body; a manual of human embryology . groove, while each lateralwall is divided into a dorsal and ventral zone by a grooveknown as the sulcus Monroi(Sm), which extends forwardand ventrally toward thepoint of origin of the opticevagination (Fig. 224). Atthe posterior end of the ridge-like elevation which repre-sents the roof-plate is arounded elevation (Fig. 223,p) which, in later stages,elongates until it almostreaches the dermis, forminga hollow evagination of thebrain roof known as thepineal process. The distalextremity of this process en-larges to a sac-like structurewhich later becomes lobed, and, by an active proliferation of the cells lining the cavi-ties of the various lobes, finally becomes a solid structure,the pineal body. The more proximal portion of the evag-ination, remaining hollow, forms the pineal stalk, and theentire structure, body and stalk, constitutes what isknown as the epiphysis. The significance of this organ in the Mammalia is the Reptilia and other lower forms the outgrowth is double,. Fig. 222.—Transverse Sec-tion OF THE THALAMENCEPH- alon of an Embryo of , Dorsal zone; fp, floor-plate;rp, roof-plate; Sm, sulcusMonroi; vz, ventral zone.—(His.) 4l6 THE DEVELOPMENT OF THE HUMAN BODY. a secondary outgrowth arising from the base or from theanterior wall of the primary one. This anterior evaginationelongates until it reaches the dorsal epidermis of the head, and,here expanding, develops into an unpaired eye, the epidermiswhich overlies it becoming converted into a transparent the Mammalia this anterior process does not develop and theepiphysis in these forms is comparable only to the posterior pro-cess of the Reptilia. In addition to the epiphysial evaginations, another evagina-tion arises from the roof-plate of the first brain vesicle, furtherforward, in the region which becomes the median portion of thetelencephalon. This paraphysis, as it has been called, has beenobserved in t
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectembryol, bookyear1902
