204 
RESPIRATION. 
of muscular power being required only to finally accomplish the 
act. When, however, respiration is quick and tumultuous, from 
whatever causes (and which I intend to enumerate by-and-by), 
powerful auxiliary agents are required. The whole of the abdo- 
minal muscles assist to effect complete expiration by compression 
of the abdominal contents against the muscular partition opposed 
between them and the lungs ; and this power of expelling air 
from the lungs by the abdominal muscles is invested in them to 
a much greater degree than at first view may be observed. 
Through the medium of the interposing viscera, the diaphragm is 
sometimes forced forward into the chest to an unusual extent, and 
powerful expiratory acts are observed in snorting, sneezing, and 
coughing. A limit, however, is set to a collapse of the lungs, by 
the rigid and unyielding tissues of the walls of the chest, and 
diminution in the capacity of the thorax cannot be carried beyond 
a certain extent, or complete collapse of the lungs takes place so 
long as the cavity is entire. 
My readers may think the above enumeration of the agents of 
respiration somewhat prolix, but the necessity for an exact con- 
sideration of them will be observed as 1 proceed with the subject. 
The principal object in the consideration of this article is the 
characters of respiration. Having first described the machine, 
and secondly the mechanism of it, the next intention is to illus- 
trate its operations by a description of the signs adduced both in 
health and disease. This brings me first to remark upon the pro- 
per development of the organs of respiration and their characters, 
as best enabling the animal to perform his most arduous achieve- 
ments, and accomplish rapid and continued exertion at the least 
expense to his system. Most horsemen, either on the turf, the 
field, or the road, are acquainted with most of the external points 
essential to good wind in horses ; but this is not enough for the 
veterinary surgeon to know. He must penetrate deeper than the 
surface, otherwise his knowledge, like theirs, will be but superficial. 
The best conformation of the chest for respiration consists 
in its great length, depth, and breadth. Every horse has the 
same number of ribs, but they are very differently formed and 
affixed to the spine and sternum. The ribs should be broad, 
their superior angles well advanced outward and backward from 
the spine, well separated from each other in their interstices, and 
of good length. The cartilages also of the true ribs should be long, 
giving depth at the sternum. In a chest thus constituted, the 
fibres of the intercostal muscles would be long — the diaphragm 
broad and powerful — the other costal muscles would be extensive 
— the attachments of the external abdominal oblique would be 
proportionately large, as would the whole of the respiratory mus- 
