AS TO SOUNDNESS. 153 



Active. . . Broncheoles. 



^ . , Residual air in air cells. 

 Passive. -^ ^, . „ . . 



Elastic walls of air cells. 



{ 



Diaphragm. 



{ 



Active. . ^ , , 



Intercostal muscles. 



Nostrils. — These should have a wide enough opening, 

 and the muscles ought to be in good tone, otherwise a 

 flapping noise like a sheet in a wind takes place. When 

 they are rigidly open they are somewhat cone-shaped — 

 the base of the cone being the opening and the apex of 

 the cone being at the part where the fleshy structure gives 

 place to the bony canal. When this cone is too small 

 and the nostrils consequently thrown into rigid contrac- 

 tion, a loud blowing noise results, and the horse is then 

 known as a " high blower." 



Turbinated bones. — These and others form a rigid 

 channel through which all the air must pass, and their 

 lining is so frequently involved in inflammation during 

 catarrh and other diseases, when inflammatory thicken- 

 ing results. This gives rise to a whistling noise during 

 inspiration and expiration, and the horse is said to 

 be a " whistler." If the membrane (schneiderian) is 

 active at the time and the parts well lined with thick 

 mucous, it gives rise to a moist rattling whistle. Should 

 there be ulceration and loss of the turbinated bones, 

 and the channel by this means widened, a loud snoring 

 results, which can be heard when the horse is standing 

 quietly in his stall. Nasal polypi are sometimes present 

 in this neighbourhood, which discover their presence by 



