. A laboratory manual and text-book of embryology. Embryology. Eponychium ~"Nail matrix * -Nail fold Nail bed Fig. 296.—Figures showing the development of the nail. A and B, in surface view; A in a 4 cm., B, in a 10 cm. fetus; C, longitudinal section through the nail anlage of a 10 cm. fetus. X 24 (Kollmann's Handatlas). of the nail substance and its surface of contact with the nail is thrown into parallel longitudinal folds. These folds produce the longitudinal ridges of the nails. The nails of man are the homologues of the claws and hoofs of other mammals. During the third month thicken
. A laboratory manual and text-book of embryology. Embryology. Eponychium ~"Nail matrix * -Nail fold Nail bed Fig. 296.—Figures showing the development of the nail. A and B, in surface view; A in a 4 cm., B, in a 10 cm. fetus; C, longitudinal section through the nail anlage of a 10 cm. fetus. X 24 (Kollmann's Handatlas). of the nail substance and its surface of contact with the nail is thrown into parallel longitudinal folds. These folds produce the longitudinal ridges of the nails. The nails of man are the homologues of the claws and hoofs of other mammals. During the third month thickenings of the integument over the distal ends of the metacarpals and metatarsals become prominent. These correspond to the touch-pads on the feet of clawed mammals. Similar pads are developed on the under sides of the distal phalanges. THE HISTOGENESIS OF THE NERVOUS TISSUES The primitive anlage of the nervous system consists of the thickened layer of ectoderm along the mid-dorsal line of the embryo. This is the neural plate (Fig. 297 A, B) which is invaginated to form the neural groove. The edges of the neural plate come together and form the neural tube (Fig. 297 C, D). The cranial portion of this tube enlarges and is constricted into the three primary vesicles of the brain (Fig. 306). Its caudal portion remains tubular and con- stitutes the spinal cord. From the cells of this tube and the ganglion crest con-. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Prentiss, Charles William, 1874-1915. Philadelphia, London, W. B. Saunders
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectembryology, bookyear1
