THE TEETH 43 



In trephining for the removal of the second molar the operator 

 must be on his guard against injuring the angular artery and vein. 

 These are frequently of considerable size, and they pass slightly 

 behind and below the seat of operation indicated. 



With regard to the amount of muscular tissue to be removed or 

 incised, the operations on the sixth and fifth molars present no difficulty, 

 since we have in the former case only the thin aponeurotic origin 

 of the levator labii superioris alicque nasi muscle. In the latter case 

 we have the upper extremity of the levator labii superioris proprius. 

 This extremity is very thin, and consequently in the two cases mentioned 

 very little hsmorrhage from muscle need be expected. But in dealing 

 with the third and fourth molars, the levator labii superioris proprius 

 is much thicker. It is, however, easily displaced in the forward 

 direction, and this is a method of procedure which is to be preferred 

 to the making of an incision through the muscle. 



The areas for operation on the first and second molars 

 are covered by the muscular portion of the levator labii superioris 

 alaeque nasi. This muscle is spread out over the seats, and more- 

 over is not easily displaced on account of its extensive aponeurotic 

 attachment to the bones. It must therefore be incised. The operation 

 is carried out with a minimum amount of hasmorrhage, if, after the 

 flap of skin has been reflected, the incision in the muscle is made 

 downwards and forwards, taking the direction in which the muscle 

 fibres run. 



Plate XI. represents the direction taken by the roots of the molars 

 of the lower jaw. As in the case of the corresponding tooth in the 

 upper jaw, the root of the sixth molar projects obliquely backwards, 

 and of course in this case downwards. The seat of operation is situate 

 two inches upwards and forwards from the most prominent point 

 of the angle of the inferior maxilla. 



It will be remembered from our superficial examination of this part 

 that this area is clothed by the masseter muscle. This muscle has 



