Chap. vii.] THE LOWER JAW. 95 



artery. The deep facial vein from the pterygoid 

 plexus will probably be cut, and, lastly, near the 

 palate will also be divided the large palatine nerve 

 and the descending palatine artery. 



It will be seen that no large artery is divided in 

 the operation. The inferior turbiiiated bone comes 

 away, of course, with the maxilla. 



The inferior maxilla. Fracture. This bone 

 is to a great extent protected from fracture by its horse- 

 shoe shape, which gives it some of the properties of a 

 spring, by its density of structure, by its great 

 mobility, and by the buffer-like inter-articular carti- 

 lages that protect its attached extremities.. The bone 

 is usually broken by direct violence, and the fracture 

 may be in any part. The symphysis is rarely broken, 

 on account of its great thickness. The ramus is pro- 

 tected by the muscular pads that envelope its two 

 sides, and the coronoid process is still more out of the 

 risk of injury, owing to the depth at which it is 

 placed and the protection it derives from the zygoma. 

 The weakest part of the bone is in front, where its 

 strength is diminished by the mental foramen, and by 

 the large socket required for the canine tooth. It is 

 about this part, therefore, that fracture is the most 

 common. The bone may be broken near, or even 

 through, the symphysis by indirect violence, as by a 

 blow or crushing force that tends to approximate the 

 two rami. Thus, the jaw has been broken near the 

 middle line by a blow in the masseteric region. The 

 amount of displacement in fractures of this bone varies 

 greatly, and is much influenced by the nature and 

 direction of the force. In general terms, it may be 

 said that, when the body of the bone is broken, the 

 anterior fragment is drawn backwards and downwards 

 by tihe jaw depressors, the digastric, mylo-hyoid, 

 genio-hyoid, and genio-hyo-glossus ; while the hinder 

 fragment is drawn up by the elevators of the jaw, 



