_Leg Musculature._--The muscles of the thigh are noticeably larger in birds that have long leg bones. (See Table 12 for size of muscles.) On the tibiotarsus, the peroneus and gastrocnemius muscles were measured. When expressed as a percentage of the weight of the bird, the peroneus has much the same relative weight in all but one of the species, whereas the gastrocnemius varies much. The peroneus is proportionately large only in _Phainoptila_, in which genus all the leg muscles are well developed, but the gastrocnemius is larger in all the Ptilogonatinae and in _Dulus_ than it is in the specialized _Bombycilla_, in which it has probably been reduced as the leg bones and other muscles have been reduced. The volume of the muscles of the hind limb changes more readily in response to saltation and running than do the muscles of the forelimb to flying. DIGESTIVE TRACT The digestive tract is relatively uniform in all genera of the family; there are only slight differences between the species. The degree of compactness of the visceral mass varies, _Phainoptila_ and _Ptilogonys caudatus_ having the folds of the digestive tract loosely arranged, whereas _Ptilogonys cinereus_ and _Phainopepla_ have folds which adhere more tightly to the ventriculus and liver. In _Dulus_ and _Bombycilla_, as compared with the Ptilogonatinae, the visceral mass (primarily liver and ventriculus) is situated more posteriorly in the body cavity, and is more compact, and the intestine is more tightly coiled. The coiling of the intestine, if its degree of compactness is disregarded, is nearly identical in the birds of the family; there are four major loops between the ventriculus and the anus. The length of this section of the tract is, however, somewhat variable, as can be seen by reference to Table 13, in which the actual and relative lengths of the intestine are given. It may be seen that in _Bombycilla_ and in _Phainopepla_, the tracts are much shortened. This is notable, since these are frugivorous birds, and in many frugivorous birds, the tract is lengthened for better extraction of edible portions of the food. Possibly the action of the digestive juices is correspondingly more rapid in _Bombycilla_ and _Phainopepla_, thereby permitting the necessary nutriment to be extracted by a short digestive tract. In a migratory bird, or one that depends on flight power to find food and escape capture by predators, as in the case of the waxwings, the compacted and shortened visceral mass would seem to be advantageous, because of the consequent reduction in weight. I consider the longer intestine to be the ancestral condition, and that the intestine has become shorter to meet new environmental conditions. Table 13. Digestive Tract: Actual Length, and Length Relative to Thoracic Length