The development of the human body; a manual of human embryology . come bulged out into two protuberances (h) which rap-idly increase in size and giverise eventually to the twocerebral hemispheres, whichform, together with the por-tion of the vesicle which liesbetween them, what istermed the telencephalon orfore-brain, the remainder ofthe vesicle giving rise to whatis known as the diencephalon(thalamencephalon) or tween-brain (Fig. 216, t). The mid-dle vesicle is bodily convertedinto the mesencephalon or mid-brain (m), but the posteriorvesicle differentiates so thatthree parts may be recog-nize
The development of the human body; a manual of human embryology . come bulged out into two protuberances (h) which rap-idly increase in size and giverise eventually to the twocerebral hemispheres, whichform, together with the por-tion of the vesicle which liesbetween them, what istermed the telencephalon orfore-brain, the remainder ofthe vesicle giving rise to whatis known as the diencephalon(thalamencephalon) or tween-brain (Fig. 216, t). The mid-dle vesicle is bodily convertedinto the mesencephalon or mid-brain (m), but the posteriorvesicle differentiates so thatthree parts may be recog-nized: (1) a rather narrowportion which immediatelysucceeds the mid-brain andis termed the isthmus (»);(2) a portion whose roof andfloor give rise to the cerebel-lum and pons respectively,and which is termed the metencephalon or hind-brain imt);and (3) a terminal portion which is known as the medullaoblongata, or, to retain a consistent nomenclature, themyelencephalon or after-brain (my). From each of thesesix divisions definite structures arise whose relations to. Fig. 216.—Reconstruction ofthe Brain of an Embryo MM. h, Hemisphere; i, isthmus; m,mesencephalon; mf, mid-brainflexure; mi, metencephalon;my, myelencephalon; nf, neckflexure; ot, otic capsule; op,optic evagination; t, thala-mencephalon.—(His.) THE BRAIN. 405 the secondary divisions and to the primary vesicles maybe understood from the following table and from theannexed figure (Fig. 217), which represents a median lon-gitudinal section of the brain of a fetus of three months. /Myelencephalon Medulla oblongata (I). 1st Vesicle, .. . j Metencephalon J Pons (II 1). (Cerebellum (II 2).Superior peduncles of theIsthmus ( cerebellum (III). (Crura cerebri (posterior por-tion).i-Crura cerebri (anterior por- 2d Vesicle Mesencephalon j tion) (IV 1). <- Corpora quadrigemina (IV 2).r Pars mammillaria(V 1).Diencephalon i Optic thalamus (V 2). I Epiphysis (V 3).3d Vesicle, .....) / Tnfundibuium (VI l). Telencephalon ^pus
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectembryol, bookyear1902
