The next point which demands attention is the =position of the operator and patient=. The chair should be placed before a good light, and if a proper dental chair is not to hand an ordinary arm chair may be utilised; failing this, two ordinary chairs may be placed back to back, on one of which the left leg of the operator should be raised to form a rest for the patient’s head. The patient should be placed in such an unconstrained position as will allow the operator to exert all necessary movements with freedom. [Illustration: FIG. 13.] [Illustration: FIG. 14.] The operator should place himself so as to use his force to the greatest advantage. His left arm may be utilised, if necessary, for steadying the movements of the patient’s head, while the fingers of the left hand can be employed-- (1) To keep the cheek and other soft parts away so as to obtain a clear view of the tooth to be extracted and its immediate neighbours; (2) To support the mandible; (3) To grasp the alveolus and so allow some idea to be gained of the effect of the force employed. The special positions for the removal of different teeth will be described in chapter ii. It may be advantageous, before describing the steps of the operation of extraction, to refer briefly to a few =points in the anatomy of the teeth and jaws= which have a direct bearing upon the manner of carrying it out. If the teeth be examined it will be noticed that they are capable of division into-- (1) Teeth with single, rounded tapering roots; (2) Teeth with single roots more or less irregularly flattened or curved; (3) Teeth with multiple roots. Under (1) are included the upper incisors (temporary and permanent) and the lower bicuspids; (2) the lower incisors and canines (temporary and permanent), and also the upper canines and bicuspids; (3) the upper and lower molars (temporary and permanent) and frequently the first upper bicuspids.[2] The shape of the roots, as we shall subsequently find, has an important bearing upon the manner in which force is to be applied when severing them from their attachments. A correct acquaintance with the disposition of the alveoli of the teeth is of importance for skilful and successful operating. Fig. 15 gives a general idea of the appearance of the alveoli, but it is needless to say that a full knowledge can only be really obtained by a careful study of the bones themselves; by this means, too, some idea of the strength of different portions of the alveolar borders can be obtained--a matter of some moment when applying force in the process of removing a tooth from its socket. The points to be specially noted in the maxilla are the thinness of the outer alveolar wall as compared with the inner, the prominence of the canine socket, and the cancellous character of the bone in the region of the third molar. In the mandible the outer alveolar border will be seen to be thinner than the inner, with the exception of that portion in the region of the