290 OPERATIONS ON BONES. 



safe plan will be to j^artly sej^arate the disk with a partial, obhque 

 turn of the trephine, and to complete the separation with the 

 elevator. Sometimes this segment will be retained in the crown 

 of the instrument, or, again, it will be only jiartially loosened. In 

 that case, securing it with a pair of bull-dog forceps, its excision 

 can be made complete with the bistoury, by dividing the mucous 

 membrane of the sinus which may hold it. If the edges of the 

 opening in the bone are not perfectly smooth, their asperities 

 should be removed with the bone scrapers or bone knives. 



The indications following the perforation of the bone vary 

 according to the case. If it is a fracture, with pushing in of the 

 bone, the fragments, or the bone debris, must be removed by 

 being raised with the bone elevator, cutting from within outward. 

 If a removal of a parasite of the cranial cavity is to be effected, its 

 membranous envelopes may be carefviUy twisted around the jaws 

 of the forceps, and thus removed in a single mass. In cleansing 

 out a purulent collection in the sinus, it must be injected and 

 washed with the proper medicated solution. If, on the contrary, 

 the removal of a foreign body is necessary, as a polypus, or an 

 odontoma, or the extraction of a molar tooth by gouging, it may 

 become necessary to enlarge the opening. This is done either by 

 chipping off the edges with the bone forceps, or by making another 

 opening with the trephine, adjoining the first, and merging them 

 together by properly trimming and shaping them. 



The dressings required after trephining vary according to cir- 

 cumstances. If the trephining has been but a preliminary step 

 to a subsequent manipulation, such as the raising of a fragment 

 of fractm-ed bone, or for the removal of foreign bodies, the wound, 

 after beino- thoroughly and antiseptically washed, can be closed 

 by bringing the edges of the integument together by sutures, and 

 covering the surface with a pad of oakum, kept in place by a fig- 

 ure 8 roller, around the head, or by one of the frontal, single or 

 double, already described. If, however, the operation has been 

 performed in a locality where there would be difficulty in retain- 

 ing such a dressing, the application of agglutinating preparations 

 or plasters will effect the object. 



When the frontal and maxillary sinuses have been opened, and 

 it becomes necessary to wash out their cavities by injections thrown 

 into them, the trephined opening must be prevented from closing 

 by the introduction of a tent of oakum and a kind of soft cork, 



