. The science and practice of dental surgery. h case to make possible acomplete reconstruction of the form of the jawsand position of the teeth. The writer devisedsuch a system of measurements, but the in-accuracies caused by taking some of themthrough the soft parts exceeded the limits ofvariation in different jaws. The difficulty isprobably not insuperable and undoubtedlycontains the solution of some of the problemsof aetiology. Tlie prosopometer, designed bySim Wallace and modified by G. Northcroft,is a useful instrument for obtaining definiteinformation with regard to relative dimensionsof
. The science and practice of dental surgery. h case to make possible acomplete reconstruction of the form of the jawsand position of the teeth. The writer devisedsuch a system of measurements, but the in-accuracies caused by taking some of themthrough the soft parts exceeded the limits ofvariation in different jaws. The difficulty isprobably not insuperable and undoubtedlycontains the solution of some of the problemsof aetiology. Tlie prosopometer, designed bySim Wallace and modified by G. Northcroft,is a useful instrument for obtaining definiteinformation with regard to relative dimensionsof jaws and arches (see pp. 144, 145), and someof the results of its application are found in theReport of the Committee of the British Societyfor the Study of Orthodontics on Phenomenafound in Post-normal Occlusion, presentedby J. G. Turner (157). The investigations ofRushton (139) on the mandibular and profileangles , and his methods of measurement, havebeen previously referred to (p. 117). A pieceof apparatus has been designed by Joh. Groth. Fig. 241.—Lingual occlusion of right lower molars. Excessive overbiteof incisors. (G. Northceoft.) (81) for measuring the different portions of theface and jaws, the angle of the mandible, andthe angular relation of other parts. CHAPTER YT ABNORIVIALITIES OF POSITION {continued) Paet VDiagnosis It has been already remarked that similarcauses may produce, or at least assist iiiproducing, very different types of abnor-mality; and, on the other hand, that casesthat appear to resemble one another closelymay be really quite diSerent in origm. Onlydeformities of a very simple type can be tracedto the action of a single cause. In most casesthe effect of one main influence in producingsome deviation from normal development isassisted or opposed by various minor conditionsor contributory causes. Therefore it is not tobe wondered at that the task of analysmg anddefuiing the abnormalities that go to composea complex case is often difficult. Still m
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