. Quain's elements of anatomy . wide openings, which afterwards are narrowed,but so as to allow the contained sacs to cohere with the gum along the border ofthe jaw. The alveoli are formed subsequently around the fangs of the teeth asthese become developed, and the jaw is deepened by the growth of its alveolarborder. The dental sacs are well seen in the jaw of an infant a few months old,before the eruption of the teeth. They are represented at this stage in fig. consist of an outer fibro-vascular coat connected with the periosteum, andan inner highly vascular layer with a little jelly
. Quain's elements of anatomy . wide openings, which afterwards are narrowed,but so as to allow the contained sacs to cohere with the gum along the border ofthe jaw. The alveoli are formed subsequently around the fangs of the teeth asthese become developed, and the jaw is deepened by the growth of its alveolarborder. The dental sacs are well seen in the jaw of an infant a few months old,before the eruption of the teeth. They are represented at this stage in fig. consist of an outer fibro-vascular coat connected with the periosteum, andan inner highly vascular layer with a little jelly-like tissue interposed betweenthe two. The inner coat is lined with the epithelium of the enamel organ to behereafter described. Their blood-vessels are derived partly from the dentalarteries which course along the base of the sacs, and partly from those of thetjums. Their extreme vascularity doubtless has relation to the nutrition of theenamel organ. Fig. 482. Fig. 482.—The dental sacs BXPOSED IN THE JAW OF ACHILD AT a, tte left lialf seen fromthe inner side ; h, the righthalf seen from the outerside ; part of the bone hasbeen removed so as to ex-pose the dental sacs as theylie below the gum; the loweriiguie shows the sacs of themUk-teeth and the first per-manent molar, exposed byremoving the bone from theoutside ; the upper figureshows the same from the in-side, together with the sacsof the permanent iucisor andcanine teeth adheiinEr to the The papilla3, now become the dental pulps, acquire a perfect resemblance to thecrowns of the future teeth, and then the formation of the hard substance com-mences in them, as will be immediately described. This process begins very early,and by the end of the fourth month of foetal life thin shells or caps of dentine(fig. 483) are found on all the pulps of the milk-teeth, and a little later on thatof the first permanent molar, while at the same time the coating of enamel beginsto be deposited on each. The cap of dentine increases
Size: 2750px × 909px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., boo, bookcentury1800, booksubjectanatomy, booksubjecthumananatomy
