Elementary anatomy and physiology : for colleges, academies, and other schools elementaryanato00hitc Year: 1869 AND PHYSIOLOGY 53 from soVoth to -TVTrd of an inch in diameter. The en- amel is also covered by a very thin membrane, TIf 5 7st of an inch in diameter, called Nas- myth's membrane. This is a ' calcified' membrane and can be seen only with great care, since it is not acted up- on by the strongest acids or alkalies. 121. Development of Teeth. ^Temporary Set. Permanent Set.—The teeth in the human subject are not perfectly formed at birth, but exist in the form of follicles or shut sac
Elementary anatomy and physiology : for colleges, academies, and other schools elementaryanato00hitc Year: 1869 AND PHYSIOLOGY 53 from soVoth to -TVTrd of an inch in diameter. The en- amel is also covered by a very thin membrane, TIf 5 7st of an inch in diameter, called Nas- myth's membrane. This is a ' calcified' membrane and can be seen only with great care, since it is not acted up- on by the strongest acids or alkalies. 121. Development of Teeth. ^Temporary Set. Permanent Set.—The teeth in the human subject are not perfectly formed at birth, but exist in the form of follicles or shut sacs, which at the seventh or eighth month of infantile life, are developed into teeth. The process of dentition generally occupies from one to three years, during which time the temporary set, as it is termed, make their appearance. These number twenty, ten in each jaw, and between the age of seven and fourteen become loose, and are easily removed to give place to the per- manent set which numbers thirty-two. Generally, however, the last tooth in each jaw does not make its appearance until the twentieth year of life. 122. A more accurate statement of dentition of the tempo- rary teeth shows that they appear at the following ages: The Incisors, from the fall to the 10th month. The Anterior Molars, 12th ' 13th ' The Canine Teeth, 14th ' 20th ' Posterior Molars, 18th ' 36th ' 123. The permanent teeth appear as follows: Fig. 65. A portion of the Surface of the Enamel on which the Hexagonal Terminations of the Fibres are shown ; highly magnified. 1 2, 3, Are more strongly marked dark, crooked Crevices, running between the rows of the Hexagonal Fibres. Describe each of the teeth. What membrane completely covers the outside of the tooth? 121. Illustrate the development of the teeth. 122. Give the time of appearance of the temporary teeth. 123. When do the permanent teeth appear ?
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