224 MEMOIRS OF T HE NATIONAL ACADEMY OF SCIENCES. 



tains, is due, not to the direct but to the inverse action of the muscle, produced under the influ- 

 ence of repeated, almost constant work. He shows that the flattening is not similar to that 

 observed hi the anthropoids; that it results from the action of a different set of muscles; that it is 

 not one of the "simian characteristics" which we are so prone to find in races whom we consider 

 inferior to ourselves; that it is an evidence not of inferiority, but of superiority, since it is pro- 

 duced under the influence of a cause essentially human. 



This inverse action of the tibialis posticus is exerted when the foot is fixed and the tibia raised, 

 as in the act of rising from a kneeling position. " This traction," says the reviewer, probably fol- 

 lowing Manouvrier, "is produced in the upright position; more still in walking, above all up 

 inclined planes, both in mounting and descending them, and infinitely more in running and jump- 

 ing. It is, therefore, very probable that platycnemia should be found in great walkers, amongst 

 the peoples of a varied country, living a savage life, hunting, etc. Children not presenting it 

 shows it to be an acquire'd characteristic which is developed only at a certain age, under the 

 influence of special conditions. We can explain thus why it is less marked in the women, and why 

 it presents in a given race very different individual degrees." 



All the above suggestions as to causal activity are pertinent; but it seems to us that one of 

 great importance remains to be made. When the tibialis posticus assumes the inverse action, the 

 tibia becomes a lever 'of the second class, with the fulcrum at the ankle joint, the power at the 

 insertion of the muscle, and the weight (which in ordinary cases is but the weight of the body and 

 the clothing) at the knee-joint. There are three ways (besides frequency of impulse) in which the 

 muscle that supplies the power may be called into increased action: First, by increasing the dis- 

 tance through which the lever moves, as in climbing hills; second, by diminishing the time in which 

 it moves, as in running and jumping; third, by increasing the weight, as in lifting and carrying 

 heavy loads. Largely to the third way we are inclined to attribute the prevalence of platycnemia 

 among various American races, including the Saladoans. The latter lived in a wide plain some 

 distance (10 miles at Los Muertos) from the nearest mountains, which are neither remarkably 

 high nor steep, and it is probable that, except for religious pilgrimages, they resorted rarely to 

 these barren summits as unproductive, no doubt, in ancient days as they are now. The Sala- 

 doans were, then, not mountain-climbers. As they did not subsist to any great extent 011 game, 

 their exercise in running was probably mostly confined to their sports. But they had no large 

 domestic animals and were obliged to be their own burden-bearers. The burdens, too, were not 

 dragged after them in vehicles, but were carried on the head or the back. Thus was the harvest 

 brought home; thus were the materials collected and elevated to construct their tall houses, and 

 the earth that was taken from their vast canals and reservoirs was carried out in baskets on the 

 backs of men and women. The work done in this way by the Saladoaus must have been enormous. 



We have now in mind many facts connected with the customs of other peoples which tend to 

 strengthen this theory, but we will not take the present occasion to mention them. To those 

 who are considering the problem of platycnemia in Europe we would suggest that they inquire 

 what effect the introduction of large beasts of burden may have had on the form of the human 

 tibia, and what effect such occupations as those of the porter and the hod-carrier may have in 

 preserving the flattened form to a limited extent to the present generation. 



We have not seen elsewhere noted a feature that is apparent on a slight inspection of the 

 bones of this series, namely, that there is a flattening of the fibula which corresponds with that of 

 the tibia. This correspondence is general but not uniform, i. e., while no constant ratio can be 

 shown to exist between the indices of associated leg bones, a very flat tibia is generally accom- 

 panied by a very flat fibula, an average tibia by an average fibula, and a normal tibia by a normal 

 fibula. The index of the fibula is usually less than that of its companion tibia. To elucidate these 

 points we give a short table, in preparing which we have selected for illustration, from the Salado 

 series, two very flat, two average, and two normal tibim. We have added one European tibia. 

 All are from the right side. 



