372 DISEASES OF BREATHING. 



The superior maxillary sinus, which is the largest, extends below the eye, 

 supposing the head to be held in a vertical position. 



The inferior maxillary sinus is usually separated by a bony partition from 

 the superior maxillaiy sinus, below which it extends not lower down than 

 the end of the zygomatic ridge. 



NATURE AND SYMPTOMS.— The commonest cause of ozeena 

 is a nasal catarrh in which the discharge has a tendency to dry in 

 the air-passages of the head in the form of hard crusts, which emit 

 the characteristic odour. In the large majority of cases, the dis- 

 charge comes from only one nostril ; that, usually, being, for 

 reasons unknown to me, the left one. As regards treatment, it is 

 important to recognise the fact that the diseased condition of which 

 nasal gleet is a symptom, may be confined to the mucous membrane 

 which lines the air-passages of the head, or may also extend to 

 that of the sinuses. The discharge, under ordinary circumstances, 

 will at first resemble that of acute nasal catarrh (p. 367), at which 

 stage the name of nasal gleet cannot be applied to it. In time, the 

 inflammation will lead to ulceration of the invaded mucous mem- 

 brane, with the formation of pus, which may more or less block up 

 the passages that drain the sinuses into the nose; thus causing 

 irregularity in the amount of the discharge. As pus dissolves the 

 tissues with which it comes in contact (p. 15), its retention in thai 

 sinuses will be followed by more or less destruction of their walls. 

 Hence it may happen that the bones which cover an abscess thus 

 formed in a sinus of the head, may become eaten away, and the 

 affected part of the face altered in appearance from the bulging 

 out of the abscess. The products from this diseased action, especi- 

 ally when bone is implicated and the discharge has been retained 

 for some time, will have a foetid smell. The gleet may be more or 

 less mixed with blood. The pus may become dried and caked in 

 the sinuses. 



As the discharge of glanders often resembles that of nasal gleet, 

 it is always well, in all cases of chronic discharge from the nose, 

 to satisfy ourselves of the absence or presence of the former disease, 

 by means of mallein (p. 626). 



In the history of a supposed cold in the head which degenerates 

 into nasal gleet, there is a watery discharge from the nose and 

 perhaps a flow of tears from the eyes. As time goes on, the dis- 

 charge from the nose assumes a pale straw colour, decreases in 

 amount, and increases in consistency, until it becomes more or less 

 like pus. Or the discharge may appear as if it were a mixture 

 of two fluids; the one watery, the other made up of debris and 

 particles of pus, which block up the passages into the sinuses from 

 time to time, and are again blown out, often with some force, 

 when the animal coughs, snorts, or breathes hurriedly from severe 



