82 ^4 Manual of Veterinary Physiology. 



respirations fall immediately the horse stops, though they do 

 not reach their normal for a few minutes. 



The ratio of heart-beats to respiration has been placed at 

 1 : 4 or 1 : 5. 



We have previously alluded to the influence of respiration 

 on the circulation, and the assistance which this renders in 

 aspirating the blood into both sides of the heart. The air 

 drawn into the veins at the root of the neck in surgical 

 operations is caused by this aspirating process. 



Movements of Nostrils and Glottis. — Before the air reaches 

 the lungs it is warmed by passing through the nasal cavities, 

 so that it enters the chest at nearly the body temperature. 

 In the majority of animals air may pass either through the 

 nose or mouth to enter the trachea, but in the horse nasal 

 respiration alone is possible; we therefore lind in this animal 

 the nasal chambers with their inlets and outlets well 

 developed. 



The opening into the nostrils of the horse is large 

 and funnel-shaped, and capable of considerable dilatation; 

 it is partly cartilaginous, and partly muscular. Imme- 

 diately inside the nostril is a large sac, which does not com- 

 municate with the nasal chamber; it is termed the false 

 nostril, and its use appears to be to simply increase the 

 capacity of the nasal opening by allowing considerable and 

 rapid dilatation. During forced inspiration the nostril ex- 

 pands, especially the outer segment, viz., that part in com- 

 munication with the false nostril, and the air is rapidly 

 drawn up through the nasal chambers. During expiration 

 the outer segment of the nostril collapses, but the inner 

 segment, composed principally of the cartilaginous ala, 

 dilates. Thus one part of the nostril is principally inspiratory 

 and one expiratory, producing a peculiar double movement 

 of the part well seen after a gallop or in acute pneumonia. 



The nasal chambers of the horse are remarkable tor their 

 great depth and extreme narrowness ; the cavities are tilled 

 up by the turbinated bones, which nearly touch the septum 

 on each side, so that a deep but extremely narrow column 

 of air passes through the chambers, tho object of which 



