Abstract
Myofibrous organization in human diaphragm muscle was studied to ascertain functional characteristics. Materials were obtained from 8 cadavers (ages 46-86, 3 males and 5 females) and separated into sternal, costal and lumbar parts. Muscle fibers were classified as white, intermediate or red by Sudan Black B stain. The following results were obtained. 1) Muscle layers were thickest in the lumbar part and thinnest in the sternal part. 2) The number of muscle fibers per square millimeter was greatest in the lumbar part. 3) The content of fiber types was 2/3 white and 1/3 intermediate. There were remarkably few red muscle fibers (about 1/30) . 4) The sizes of muscle fibers were: largest for white and smallest for red in the costal part ; similar for white and intermediate in the sternal and lumbar parts ; larger in males than in females, especially red muscle fibers. Among the three parts, the smallest fibers were in the lumbar part, for all fiber types. 5) Density of muscle fibers was about 90 % and was similar in the sternal and costal parts, and only slightly less in the lumbar part.
