DEAROLF, J.L.*; ROMMEL, S.A.; HERMANSON, J.W.: Compartmentalization of the Florida manatee (Trichechus manatus latirostris) diaphragm

Rommel and Reynolds (�00) proposed that Florida manatees may utilize unique contractions of their hemidiaphragms to determine the amount and distribution of air in their elongated lungs and thereby control their body position and pitch in the water column. However, for the manatee to be able to control air distribution in its lungs, its diaphragm must be composed of distinct elements that could be recruited individually to contract. To test this hypothesis, we examined the innervation pattern of the diaphragm as well as identified internal connective tissue elements that could divide the muscle into smaller units. In addition, we investigated the histochemical and biochemical properties of the compartments identified in the anatomical study. Detailed dissections of adult manatee diaphragms have revealed vascular/connective (v/c) tissue bundles that extend from the central tendon to the ribs. These bundles separate the diaphragm into approximately 1-cm wide blocks. We have also identified muscle fibers that are oriented parallel to the long axis of the diaphragm. These fibers insert into the v/c tissue bundles. Thus, these bundles could compartmentalize the diaphragm. However, branches of the phrenic nerve innervate groups (4-6) of the muscle blocks, not the individual units. Additionally, although the histochemical profiles of adjacent blocks are virtually identical, the profiles of non-adjacent muscle blocks (approx. 10-cm apart) are slightly different. These observations suggest that the compartments are composed of groups of the muscle blocks, a design that would give the manatee relatively fine motor control over the air distribution in its lungs. Research supported by Sigma-Xi GIAR.