It may be noted that _Phainoptila_ and _Bombycilla_ have the shortest arm in the family Bombycillidae. The humerus, radius and ulna are comparable to the same elements in thrushes and the catbird, and it is only the extremely short manus in _Phainoptila_ that affects the total. The manus in _Phainoptila_ is comparatively smaller than in any other genus of the family Bombycillidae, and this indicates poor flight power. _Bombycilla_ has a total length corresponding closely to that in warblers, but the lengths of the distal elements correspond closely to those in the catbird and thrushes. Of the three segments, the humerus is, relatively, the most shortened. Next in order of increasing length of arm is _Dulus_; measurements for it are roughly the same as those of _Myadestes_. The wing bones of the Ptilogonatinae, other than _Phainoptila_, are the longest in this series, and they most nearly resemble the same bones in flycatchers, Parids, and gnatcatchers. [Illustration: Fig. 47. Graph showing relative lengths of bones of the arm. The percentage values are shown on the axis of the ordinates. A. _Bombycilla cedrorum_; B. _Bombycilla garrula_; C. _Dulus dominicus_; D. _Phainoptila melanoxantha_; E. _Phainopepla nitens_; F. _Ptilogonys cinereus_; G._ Ptilogonys caudatus_. a. humerus; b. radius; c. ulna; d. manus; e. total.] It is notable that, in general, birds with long and narrow wings appear to have relatively the shortest humeri, with the distal bones, especially the manus, variable in length and seemingly correlated with the manner of feather attachment. Those birds with rounded and short wings have the longest humeri. In swallows, for example, the humerus is short, whereas the other arm bones are long, and the manus is unusually large and heavy. A short humerus gives better lever action in the flight stroke than a long humerus does. MUSCULATURE