Reference > Anatomy of the Human Body > Page 738
Henry Gray (1825–1861).  Anatomy of the Human Body.  1918.
the head. The lateral walls of the brain-tube, like those of the medulla spinalis, are divided by internal furrows into alar or dorsal and basal or ventral laminæ (Fig. 646).

FIG. 646– Diagram to illustrate the alar and basal laminæ of brain vesicles. (His.) (See enlarged image)

FIG. 647– Transverse section of medulla oblongata of human embryo. X 32. (Kollmann.) (See enlarged image)

FIG. 648– Transverse section of medulla oblongata of human embryo. (After His.) (See enlarged image)

The Hind-brain or Rhombencephalon.—The cavity of the hind-brain becomes the fourth ventricle. At the time when the ventral cephalic flexure makes its appearance, the length of the hind-brain exceeds the combined lengths of the other two vesicles. Immediately behind the mid-brain it exhibits a marked constriction, the isthmus rhombencephali (Fig. 650, Isthmus), which is best seen when the brain is viewed from the dorsal aspect. From the isthmus the anterior medullary velum and the superior peduncle of the cerebellum are formed. It is customary to divide the rest of the hind-brain into two parts, viz., an upper, called the metencephalon, and a lower, the myelencephalon. The cerebellum is developed by a thickening of the roof, and the pons by a thickening in the floor and lateral walls of the metencephalon. The floor and lateral walls of the myelencephalon are thickened to form the medulla oblongata; its roof remains thin, and, retaining to


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