The centrum of _Dulus_ in posterior aspect presents the appearance of a simple shield; little of the indentation seen in _Bombycilla_ is present. The spinous portion is plain, with no constriction nor terminal enlargement in the neck. The centrum in _Phainopepla_ is similar to that in _Dulus_, but has a small expansion at the base of the spine, the entire centrum being wider in proportion to its over-all size than in any of the other species mentioned previously. The centrum in _Ptilogonys_ shows great width, and the spine is in a large expanded tip as in _Bombycilla_. The lateral edges of the centrum in _P. cinereus_ are "winged" and in two separate halves; whereas the centrum of _P. caudatus_ is fairly plain, its specialization being reflected primarily in breadth and flatness. In cross section of the centrum, _Phainoptila_ is similar to _Phainopepla_, although, in the former, the bone is smaller in proportion to the size of the animal, and the lateral wings are more angular than in _Phainopepla_. [Illustration: Figs. 36-42. Pygostyles in lateral view of five genera of Bombycillidae. x 2. 36. _Phainoptila m. melanoxantha_, sex?, MNH no. 26493, 15 mi. SE Cartago, Costa Rica. 37. _Ptilogonys caudatus_, male, MNH no. 24492, 15 mi. SE Cartago, Costa Rica. 38. _Phainoptila nitens_, male, MNH no. 24754, Pima Co., Arizona. 39. _Ptilogonys cinereus_, female, Louisiana State University no. 297, Xilitla Region, San Luis Potosi, Mexico. 40. _Dulus dominicus_, female, USNM no. 292652, Don Don, Haiti. 41. _Bombycilla cedrorum_, male, MNH no. 15331, Bexar Co., Texas. 42. _Bombycilla garrula_, sex?, USNM no. 223895, Bozeman, Montana.] In specialization for muscle attachment, the centra of the pygostyles of the Ptilogonatinae have more area for muscle attachment than do the centra in the Bombycillinae and Dulinae; the centrum is wide, the spinous portion is long, and the bone is flattened anteriorly. The most generalized pygostyle is in _Phainoptila_, and that of _Dulus_ differs only slightly. In _Bombycilla_ the pygostyle is proportionately small, but is complex in shape; there is seemingly not the need for greatly expanded areas since the caudal muscles are less specialized in this genus. _Sternum._--The sternum in Bombycillids is typically passerine in general shape and in having a long and deep carina or sternal crest. The caudal process of the bone is broad, with the terminal ends flattened, forming dorsally a graceful V-shaped outline, whereas the outline of the posterior end of the sternum is broad and convex.