70 
TREPHINING THE FACIAL AND MAXILLARY SINUSES. 
give iise to excessive granulation. The late Professor Robertson recom¬ 
mended removing a circular patch of skin. Cicatrisation is much more 
perfect after this procedure, and in one or two months no visible wound 
Fig. 48.—Head of a horse. 
Ullllll | boundaries of the frontal sinus. 
,, ,, nasal meati. 
remains. In the middle of each 
edge of the wound a stitch is 
inserted, by which the flaps are 
drawn asunder. The skin is 
separated from the sub-lying 
tissues with the knife in order to 
make room for the trephine crown 
between the two edges of the 
wound. Should the operation on 
the superior maxilla be performed 
rather higher than above de¬ 
scribed, the belly of the levator 
labii superioris is encountered, 
and must be pushed to one side. 
The trephine crown is now placed 
in position, and to facilitate re¬ 
moval of the pieces of periosteum 
a cut is made around it with a 
guarded bistoury, and the mem¬ 
brane separated with a scraper or 
blunt knife. A central hole having 
been made with a gimlet, the 
trephine, with its centre pin in 
advance, is replaced in position, 
and by light rotary movements 
caused to enter the bone. The 
instrument in case of need is sup¬ 
ported by the thumb and index 
finger of the operator’s left hand. 
The teeth of the saw soon begin to 
act, but, before the piece of bone 
to be excised is loosened, the 
elevator should be inserted. The 
trephine, being again placed in 
;» » superior maxillary sinus, position, is used as before de¬ 
scribed until the bone is perforated. 
W leie the latter is very thick it will be necessary from time to time to clean 
the teeth of the trephine with a brush. An increased sense of yielding 
gradually becomes apparent, whereupon sawing is more cautiously pro” 
ceeded with. As soon as the bone is thought to be cut through, the 
