344 CLINICAL APPLIED ANATOMY. 



On the other hand, the pus may find an exit through the sub- 

 stance of the bony tissue of the jaw. In the case of the mandible, 

 if it reaches the external surface of the bone, it raises the peri- 

 osteum and collects either between that membrane and the 

 osseous tissue, or, perforating the membrane, forms a cavity in 

 the superficial soft structures. It will thus be seen that an abscess 

 of this character consists of pus in two cavities with a narrow 

 track between. The one cavity, the alveolus, is small ; the other 

 cavity, external to the bone, may be many times greater (Fig. 48). 



In order to obtain a satisfactory evacuation of the purulent 

 fluid, it is desirable that the offending tooth should be extracted, 

 to drain the alveolar cavity, and that an incision should be made 

 from within the mouth, keeping close to the bone, to open the 

 external collection. By this internal incision a disfiguring scar 

 in the skin may be prevented. Unless the knife is kept practi- 

 cally in contact with the bone, there may be some danger of 

 wounding the facial artery, near the anterior border of the 

 masseter. 



In the maxilla, pus may find its way through the bone in two 

 directions, either upwards into the antral cavity or inwards 

 beneath the muco-periosteum of the palatal process of the 

 maxilla. Pus formed in connexion with the second molar is 

 that which most commonly induces antral empyema, owing 

 to the fact that the fangs of this tooth may actually project 

 through the bony floor of the cavity and slightly raise its muco- 

 periosteum. Occasionally the roots of the first molar or second 

 bicuspid also perforate the floor of the antrum. Pus in the 

 antrum may find its exit by the side of the affected tooth into 

 the mouth, or through the opening of the antrum into the 

 middle meatus of the nose, or occasionally through the anterior 

 wall of the cavity into the tissues of the cheek. It is only, 

 however, in a certain number of instances that the purulent 

 fluid will flow into the nasal cavity, because the aperture in the 

 natural state with all the bones and the mucous membrane 

 present, is really a small one, and may be readily occluded by 

 the swelling of the soft tissues. Further, the opening lies at 



