Estimation of the cellularity of articular cartilage has usually been undertaken as a subsidiary part of investigation of the tissue metabolism. Consequently the choice of species or joint has been influenced by availability or convenience for biochemical analysis. Information has been obtained for rabbit (Bywaters, 1937;​ Barnett, Cochrane & Palfrey, 1963;​ Mankin & Baron, 1965) and human femoral condylar cartilage (Stockwell, 1967);​ human patellar and humeral head cartilage (Meachim & Collins, 1962);​ horse carpal (Bywaters, 1937) and bovine metacarpo- and metatarsophalangeal joints (Rosenthal, Bowie & Wagoner, 1941). In general it may be deduced that cartilage from smaller species is more cellular than that from larger species, and that the cartilage in small joints of large animals resembles that in large joints of small animals (Barnett, 1963). However, in the studies cited there are insufficient features in common, either in the techniques employed or in the species or type of joint investigated, to enable much useful comparison.

The present study attempts to provide more systematic data for a number of species and different joints. It is shown that there is an inverse relationship between cell density and the thickness of articular cartilage. The findings are relevant to the nutrition and to some aspects of the growth and pathology of the tissue.