Fig. 2. Subvertebral and brachial sac pressures measured for one C. marinus during a single breath. Inspiration (solid horizontal line) and expiration (broken horizontal line) are indicated above the subvertebral pressure trace. Note that subvertebral sac pressure (top trace) increases during inspiration with little or no change in brachial sac pressure (bottom trace). During expiration there is a decrease in subvertebral sac pressure that is rapidly transmitted to the brachial sac.