. A laboratory manual and text-book of embryology. Embryology. 162 THE DISSECTION OF PIG EMBRYOS FOR STUDY 157). Of the alveolo-lingual glands nine or ten may develop on either side in embryos of 40 mm. (McMurrich in Keibel and Mall, vol. 2, p. 348-349.) The branched anlages of the salivary glands are at first solid and hollow out peripherally. The glands continue growing and enlarging until after birth. Mucin cells may be distinguished by the sixteenth week and acinus cells in the parotid glands at five months (McMurrich). THE DEVELOPMENT OF THE TEETH The development of the teeth is described
. A laboratory manual and text-book of embryology. Embryology. 162 THE DISSECTION OF PIG EMBRYOS FOR STUDY 157). Of the alveolo-lingual glands nine or ten may develop on either side in embryos of 40 mm. (McMurrich in Keibel and Mall, vol. 2, p. 348-349.) The branched anlages of the salivary glands are at first solid and hollow out peripherally. The glands continue growing and enlarging until after birth. Mucin cells may be distinguished by the sixteenth week and acinus cells in the parotid glands at five months (McMurrich). THE DEVELOPMENT OF THE TEETH The development of the teeth is described in all the standard textbooks of histology and only a brief account of their origin and structure will be given here. The enamel organs, which give rise to the enamel of the teeth and are the moulds, so to speak, of the future teeth, are of ectodermal origin. There first appears in embryos of 10 to 12 mm. an ectodermal downgrowth, the dental ridge or lamina on the future alveolar portions of the upper and lower jaws (Fig. 154). These Fig. 154.—Early stages in the development of the teeth. A, 17 mm.; B, 41 mm. (Rose). LF., LFL., labial groove; Pp., dental papilla; UK., lower jaw; uL., lower lip; ZL., dental ridge. lamina; parallel and are mesial to the labial grooves, being directed obliquely toward the tongue. At intervals, on each curved dental ridge or lamina a series of thickenings develop, the anlages of the enamel organs (Fig. 155). Soon the ventral side of each enamel organ becomes concave (embryos of 40 mm.) forming an inverted cup and the concavity is occupied by dense mesenchymal tissue, the dental papilla (Figs. 154 B and 156). An enamel organ with dental papilla forms the anlage of each decidual or milk tooth. Ten such anlages are present in the upper jaw and ten in the lower jaw of a 40 mm. embryo. The connection of the dental anlages with the dental ridge is eventually lost. The position of the tooth anlage between the tongue and lip is shown in Fig. 157. T
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