Structure-function relationships of the flexor carpi radialis muscle compared among four species of mammals.

Investigations of the structure and function of the flexor carpi radialis muscle (FCR) in the cat have led to the hypothesis that the compartmentalized (nonuniform) distribution of fiber types within the muscle relate to the complex motor skills of the cat. To test this hypothesis a study was undertaken to compare the FCR in four mammalian species of similar body size but with different forelimb motor tasks. The species chosen were: dog, opossum, armadillo, and cat. Comparisons were made among species with regard to general muscle morphology, fiber types and sizes, fiber proportions, and fiber distributions. The FCR of all species was morphologically similar and contained three muscle fiber types (SO, FOG, and FG). The mean area of muscle fibers was largest in opossum, while the FCR fibers of dogs were smallest. The percentage of SO fibers in the dog FCR was greater than in the other species studied. The opossum FCR also contained a high percentage of SO fibers. The armadillo FCR consisted of a high percentage of FG fibers. In the cat FCR the percentages of all three fiber types were similar. For each species, individual fiber proportions were in agreement with the results for fiber percentages. Compartmentalized distribution of fiber types existed in each species with the dog having the most compartmentalized fiber type distribution and the cat the least compartmentalized distribution. Therefore it seems that the compartmentalized organization of the FCR is not related to any specialized motor task, but may be a generalized pattern associated with motor patterns shared among all species studied.