199 
MR. YOUATT's VETERINARY LECTURES. 
Sometimes the disease assumes a more chronic form. The 
inflammation runs on to ulceration of the membrane without this 
excessive cerebral disturbance. A purulent discharge then ap¬ 
pears from the nose, evidently not of a glanderous nature, from 
its not being viscid, and none of the submaxillary glands being 
enlarged. 
In both the acute and the chronic form, it is usually confined 
to one sinus. We are indebted to Mr. John Field, jun., for the 
principal knowledge we have obtained of this disease. 
Fluctuating* or encysted tumours are sometimes found on the 
frontal, nasal, lachrymal and superior maxillary bones, varying 
from the size of a small marble to that of a nutmeg. They con¬ 
sist of glairy fluid enclosed in a dense cyst. After a consi¬ 
derable time the cyst occasionally disappears, and the tumour 
becomes solid. They are oftenest found on half-bred horses. 
They will never ulcerate or be any serious nuisance, and should 
not be meddled with. 
When they have long existed, they may - by their pressure 
. rouse the absorbents to action, and cause a portion of the bone 
beneath to disappear. I have seen this. The periosteum alone 
remained. I had once an annoying instance of it. I was re¬ 
quested to get rid of one of larger size than usual, and of long 
standing on the forehead. I was unwilling to dissect it out at 
once, and tried first w hat puncturing it w ould effect. I lanced 
it, and deeply, rather too deeply, for my instrument penetrated 
into the frontal sinus, there being no bone left to arrest its pro¬ 
gress. It had been taken up by the increased action of the ab¬ 
sorbents, caused by the long-continued pressure of the tumour. 
It was nearly two months before I could get this little wound to 
heal, and then it was apparently effected by granulations spring¬ 
ing from the bottom of the sinus. 
The inner plate of the frontal bone is divided into two unequal 
parts, by an irregularly formed lateral septum [a section of the 
head was here shewn]. The super portion forms the su¬ 
perior and posterior part of the floor of the sinus, and the 
anterior and inferior part of the roof of the cranium. The inferior 
portion forms the super portion of the roof of the nasal cavity; 
and the anterior and inferior part of the floor of the sinus. 
The cranial portion of the frontal bone covers the anterior part 
of the brain; and there it is thickest and strongest, and espe¬ 
cially thickest where strength is most wanted, namely, at the 
centre or roof of the arch, to the security of which, next to that 
ot the base, the attention of the builder is directed. We there 
find a considerable crest or spine, extending from the cristo-galli 
of the ethmoid bone, along the frontal and the parietal bones 
to the tentorium. 
