_Caudal Muscles._--The muscles of the caudal area that were used for comparison were the levator caudae and the lateralis caudae. These muscles are used by the living bird to maintain the position of the pygostyle and therefore the rectrices; these muscles are especially important to those birds that utilize the tail as a rudder in flight and as a brake. As may be seen by reference to Table 11, the two muscles are largest in proportion to body weight in the Ptilogonatinae, in which subfamily the species have long rectrices and must have correspondingly well-developed muscles in order to utilize the rectrices to best advantage in flight. The lateralis caudae differs more according to species than does the levator caudae, showing that rudder action of the tail is of primary importance in the adaptation for capturing insects. It will be remembered that the pygostyle in this subfamily has a flattened lateral surface for attachment of the levator caudae muscle, and it is therefore to be expected that this muscle will be larger in the Ptilogonatinae than it is in either the Bombycillinae or the Dulinae. The levator coccygis, together with the two muscles mentioned above, is responsible for elevation of the tail. The levator coccygis is less altered in different species of the family than is the lateralis caudae. It may be noted that the caudal muscles of _Dulus_ and _Bombycilla_ constitute a smaller percentage of the total weight of the bird than in any of the genera in the subfamily Ptilogonatinae. [Illustration: Fig. 48. Caudal musculature, of _Phainopepla nitens lepida_, in dorsal view. x 2. a. Levator coccygis; b. Levator caudae; c. Lateralis caudae; d. Lateralis coccygis; e. oil gland; f. dorsal tip of pygostyle.] Table 11. Caudal Muscles (Actual and Relative Weights) ============================================= Species | Levator | Lateralis ------------------------+---------+---------- Ptilogonys caudatus | .145g. | .022g. | .092% | .045% | | Ptilogonys cinereus | .030g. | .010g. | .076% | .026% | | Phainopepla nitens | .025g. | .008g. | .096% | .029% | | Phainoptila melanoxantha| .040g. | .015g. | .063% | .014% | | Dulus dominicus | .028g. | .006g. | .063% | .014% | | Bombycilla garrula | .034g. | .010g. | .048% | .014% | | Bombycilla cedrorum | .026g. | .008g. | .050% | .014% --------------------------------------------- Table 12. Weights of Muscles (These percentages expressed in terms of weights of the body)