Skeletal System

The main gross differences among the mouse, rat, and human skeletal systems, in addition to size, are skull and tail morphology, and the shape and orientation of the shoulder and pelvic girdle bones. Articular cartilage is thinner in rodents, and the subchondral bone plate is more variable in thickness. Long bone growth plates generally are obliterated in late adolescence in humans; however, in rodents, growth plate remnants persist throughout life, while longitudinal bone growth ceases by about 6 months. Histologically, the basic bone remodeling processes are similar. However, mouse and rat cortical bone rarely undergoes the Haversian remodeling seen in human bone, and the mouse and rat cortex mostly comprises circumferential lamellae rather than the osteonal structures common in humans. The distribution of adipose tissue differs between rodents and humans, with brown adipose tissue much less prevalent in adult humans than in rodents.