The principles and practice of dentistry : including anatomy, physiology, pathology, therapeutics, dental surgery and mechanism / by Chapin A. Harris.

  • Harris, Chapin A. (Chapin Aaron), 1806-1860.
Date:
1910
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Licence: In copyright

Credit: The principles and practice of dentistry : including anatomy, physiology, pathology, therapeutics, dental surgery and mechanism / by Chapin A. Harris. Source: Wellcome Collection.

Provider: This material has been provided by The University of Glasgow Library. The original may be consulted at The University of Glasgow Library.

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    interior of the maxillary arch, having the form of a whitish cord situated in a bed of soft transparent tissue, and 'is composed of two symmetrical parts corresponding to the right and left sides of the lower jaw, which parts soon become united at the mental symphysis. From this point or juncture the two halves extend on either side to the bones of the ear, terminating in the malleus, which, with the incus, is formed from it. Meckel's cartilage gives form and stability to the lower jaw of the embryo, and is the first solid structure discovered in the maxillary arch. It first appears about the twenty-fifth day, and during its exist- ence, which extends to the fifth month of fetal life, it is subject to constant modifications or transitory states. Fig. 2.—Meckel's Cartilage, from Embryo of 40 to 4.2 Days, before Appearance of Maxillary Bone. a. Enlargement of cartilage near neck of malleus, d. A slightly enlarged portion of cartilage, but contracted at median line, where it unites with that of opposite side. n. Handle of malleus, o. Cartilage of the os lenticulare. /. Cartilage of the stapes, j. Outline of the jaw to be formed. As soon as the cartilage has attained its full development, a period which corresponds to the ossification of the malleus, it begins to disap- pear, except the end, which extends up to the tympanum and becomes ossified into the malleus, owing to the action of the osteoblasts by which this cartilage is ossified, and becomes a part of the maxilla. In the upper jaw the period of evolution corresponds with that of the lower jaw j Meckel's cartilage belongs exclusively to the lower' jaw. At a period between the thirty-fifth and fortieth days of embryonal life, slight traces of ossification are observed at points midway between the angle and symphysis of the future jaw, and the ossification extends rapidly in both directions, anterior and posterior, along the external face of Meckel's cartilage, and in contact but not united with it.