Thus, the divided or undivided conditions of the _m. obturator externus_ and the _pars interna_ of the _m. gastrocnemius_ seem to be correlated with the degrees of strength of certain movements of the leg. It is conceivable that these differences in structure are correlated with the manner in which food is obtained, the birds having the bipartite muscles being those which spend the most time on the ground searching and scratching for seeds and other sorts of food. Yet, in _Leucosticte_, a cardueline, and in _Calcarius_, an emberizine, whose foraging habits are rather similar, the structure is unlike. _Leucosticte_ does resemble the emberizines and also _Piranga_ and _Spzia_ in the extension of a band of muscle fibers from the _pars interna_ of the _m. gastrocnemius_ around the front of the knee. A band of muscle fibers of this sort strengthens the knee joint and gives still more strength to the _pars interna_. This condition has been reported in a number of birds by Hudson (1937) and is, in all probability, an adaptation for greater strength of certain leg movements. The development of this band in _Leucosticte_ seems to parallel that in the other birds studied and does not indicate relationship, since in _Leucosticte_ this band arises from the undivided muscle which (as stated above) resembles only the posterior portion of the bipartite muscle described for the other birds. In the latter, the muscular band arises from the anterior part of the muscle.
Minor differences in muscle pattern, like those already mentioned, are consistent also between subfamilies, but correlation of these minor differences with function is difficult. There is the implication, however, that in all the groups except the carduelines and ploceids, the emphasis is on greater strength and mobility of the leg. In the carduelines that were studied the origin of the _m. sartorius_ does not extend so far craniad as in the other species. In the latter, at least half of the origin is from the last one or two free dorsal vertebrae; in the carduelines no more than one third of the origin is anterior to the ilium. It is conceivable that the more craniad the origin, the stronger the forward movement of the thigh would be.