The animals and man; an elementary textbook of zoology and human physiology (1911) (14598225679)

Identifier: animansmanelemen00kell (find matches)
Title: The animans and man; an elementary textbook of zoology and human physiology
Year: 1911 (1910s)
Authors: Kellogg, Vernon L. (Vernon Lyman), 1867-1937 McCracken, Mary Isabel
Subjects: Zoology Physiology
Publisher: New York, H. Holt and company
Contributing Library: MBLWHOI Library
Digitizing Sponsor: MBLWHOI Library

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and ap-pear while the jaws aresmall. As the jawsenlarge (during the sixthand seventh years) thesecond set or perma-nent teeth grow in andone by one replace themilk teeth. The perma-nent teeth need muchcare and attention asthey must last through- out life. Kinds of teeth.- FIG. 1^7. Diagram of the buccal cavity showing the manner of closing the There are eight teeth in posterior nares during deglutition, the front of the mouth(After Landois & Stirling.) ^Qur Qn each -x called incisors, to bite and cut the food. The sharp pointed teethon either side of the incisors are the canines. On eitherside of the canines there are two large teeth with two-point-ed surfaces. These are the bicuspids or premolars. Oneither side of the premolars are three large molars. Thepremolars and molars are grinders. The third molars fre-quently do not appear until after the twentieth year, andare commonly called the wisdom teeth. Structure of the teeth (fig. 158).--The teeth, though as Harcl palate H Larynw
Text Appearing After Image:
Trachea/ 306 THE ANIMALS AND MAN c~ PC_Ji§ hard as bone, are not bone but a hardened epithelium tissue.The part above the gum is the crown and is but a part ofthe whole tooth. Under the gum are the neck and roots.The roots are inserted into sockets in the jaws. The in-cisors and canines have butone root, the premolars haveusually two roots and the mo-lars have from two to five. If a tooth is cut lengthwiseas shown in the figure, thereis exposed a central chamber,or pulp chamber filled withblood-vessels and nerves whichhave entered the cavitythrough the roots. The pulpchamber is surrounded by alayer of dentine (D), an ivory-like substance which makes upthe bulk of the tooth. Thedentine is protected on thecrown by enamel (E), thehardest substance in the body,and on the roots by cement(C). The enamel protectsthe teeth from mechanical FIG. 158. Vertical section of ainjury and from the effect of tooth in Jaw. E, enamel; D,chemicals and bacteria. Care of the teeth.—As theteeth masticate

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