The measurements of the lengths and widths of the skulls are given in Table 9. The relative length of the bill and relative width of the skull are given in Table 10. These relative measurements are calculated by using the actual measurements in Table 9 as numerators, the length of the skull from the lacrimal bone to the posteriormost end of the skull being used as the denominator. The data indicate that _Phainoptila_ has a slightly narrower cranium. _Humerus._--Certain families of passerine birds have a noticeable variation in the characteristics of the humerus; the bone varies in length, in diameter, and in the complexity of the processes at either end. In the Bombycillids, however, the amount of variation is relatively small, and the diaphysis of the bone is somewhat twisted, especially so in _Dulus_. The deltoid tuberosity is variable, being shorter but more elevated in _Bombycilla_ than it is in the Ptilogonatinae and in the Dulinae. The tendon from the pectoralis major muscle, which inserts on this process, probably finds better insertion on a higher process than on a lower but longer one. [Illustration: Figs. 22-28. Humeri of five genera of Bombycillidae. Natural size. 22. _Phainoptila m. melanoxantha_, sex?, MNH no. 26493, 15 mi. SE Cartago, Costa Rica. 23. _Ptilogonys caudatus_, male, MNH no. 24492, 15 mi. SE Cartago, Costa Rica. 24. _Phainopepla nitens_, male, MNH no. 24754, Pima Co., Arizona. 25. _Ptilogonys cinereus_, female, Louisiana State University no. 297, Xilitla Region, San Luis Potosi, Mexico. 26. _Dulus dominicus_, female, USNM no. 292652, Don Don, Haiti. 27. _Bombycilla cedrorum_, male, MNH no. 15331, Bexar Co., Texas. 28. _Bombycilla garrula_, sex?, USNM no. 223895, Bozeman, Montana.] Distally, the two major condyles and the intercondylar groove or olecranon fossa that make efficient articulation with the ulnar process, are not variable. The external condyle, however, is significantly variable in the family. This condyle is longest and most pronounced in birds in which the humerus is short in relation to the trunk, as for example in _Tachycineta_. In the Bombycillidae the condyle is smallest in _Phainoptila_, where it is a mere suggestion of a process. In the remainder of the Ptilogonatinae, the condyle is larger but rounded, and shows a double process in _Ptilogonys caudatus_, and a slightly pointed process in _P. cinereus_. The external condyle in _Dulus_ is not specialized, being low and rounded, but in _Bombycilla_, it is noticeably elongated, indicating a better attachment distally for the deltoid muscle. (No measurements are tabulated for this condyle, as the percentage of error in measuring this small structure is great.) Table 1 gives lengths of humeri, and Table 2 gives lengths of the humeri expressed as percentages of the length of the trunk, a standard measurement.