Dental cosmos . e combined widths of the superior central, lateral, andcuspid, taken at the lines of greatest breadth. A line, at rightangles to the median line of the head, through the center of thiscircle, which is known as the circle of the mouth, will pass throughthe centers of the second bicuspids; and a similar line, parallel tothe first, through the posterior periphery of the circle, will passthrough the posterior edges of the second molars. The cuspid and the anterior buccal cusp of the first molar, itwill be remembered, have been previously spoken of as formingrespectively the primary
Dental cosmos . e combined widths of the superior central, lateral, andcuspid, taken at the lines of greatest breadth. A line, at rightangles to the median line of the head, through the center of thiscircle, which is known as the circle of the mouth, will pass throughthe centers of the second bicuspids; and a similar line, parallel tothe first, through the posterior periphery of the circle, will passthrough the posterior edges of the second molars. The cuspid and the anterior buccal cusp of the first molar, itwill be remembered, have been previously spoken of as formingrespectively the primary and secondary springs of the superiorarch; that is, they mark decided changes in its direction. In PlateS the superior central, lateral, and cuspid, as has been said, lie inthe arc of the circle of the mouth. At the cuspid the directionchanges; the buccal faces of the teeth between the cuspid and theanterior buccal cusp of the first molar lie in a straight line. Atvol. xxxr.—43 614 THE DENTAL COSMOS. Plate S*. TYPICAL TOOTH-FORMS. 615 this latter point, which is usually prominent, the arch is againdeflected slightly inward. In the inferior jaw there is no secondary spring of the four incisors are more nearly in a straight line than their corre-sponding teeth in the superior jaw. The direction changes sharplyat the cuspid and thence forms a continuous, gentle curve along thebuccal faces of the teeth, though the lingual faces of the posteriorteeth approach very closely to a straight line. (These latter pointsdo not appear in Plate S, as the teeth were drawn in position togive a perspective instead of an exact face-view.) Conclusions. Some of the facts brought out in this investigation deserve specialattention. It is unnecessary here to comment on the perfect con-struction of each individual tooth with relation to the use it isintended to serve ; but there are a few points which it may be wellto emphasize. The cutting-edges of the incisors are, to all appearance, frail
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