=========================+========+======= | Length | Width Species | of | of | Skull | Skull -------------------------+--------+------- Ptilogonys caudatus | 160 | 72 Ptilogonys cinereus | 158 | 69 Phainopepla nitens | 162 | 73 Phainoptila melanoxantha | 161 | 65 Dulus dominicus | 164 | 75 Bombycilla garrula | 164 | 74 Bombycilla cedrorum | 162 | 74 -------------------------+--------+------- [Illustration: Fig. 43. Part of skeleton of _Bombycilla cedrorum_ showing method of measuring the length of the trunk. Natural size.] _Leg-trunk Percentages._--Table 4 shows the relative lengths of the legs and of the separate bones in the legs of the different species of the Bombycillids. Table 5 shows corresponding lengths for other passerine birds. The total length of the leg was computed by adding the figures obtained for the lengths of the femur, tibiotarsus and tarsometatarsus. The lengths of the toes were disregarded. Length of leg was recorded in this same way by Richardson (1942:333), who thought that only in swimming and running birds do the toes contribute to the functional length of the hind limb. Table 4 shows that of the birds compared in this paper, _Dulus_ has the longest legs. In order of decreasing length the others are the Ptilogonatinae, and finally the Bombycillinae, which have the shortest legs of all. In Waxwings the length of the legs, expressed as percentages of the body-lengths, are identical with those birds that are similar in habits, that is to say, birds which do not use the hind limb except in perching. It can be noted by reference to Table 5 that _Tachycineta_ and _Myadestes_ fall into this category. This shortness of limb is obviously adaptive, and each of the segments of the limb has been correspondingly shortened, with no element reduced at the expense of the other two. The short leg can be more easily folded against the body while the bird is in flight, than can a long leg which is more unwieldy. It may be noted from tables 4 and 5 that birds which spend much time on the ground, or that hop a great deal in the underbrush, have longer legs than do birds which spend much time in flight. Two birds with noticeably long legs are _Hylocichla mustelina_, a typical ground dweller, and _Parus atricapillus_, which hops about in the trees and underbrush.