the Structure of Hierococcyx S^c. 601 



of them entirely disappear. Thus in Hierococcyx, in 

 Cuculus, and in the allied genus Cacomantis the ventral tract 

 of either side ends in a single row of feathers through the 

 suppression of the two rows which are found in addition 

 higher up in the tract. 



The second feature which I believe to be of importance for 

 purposes of classification is that afforded by the muscles of 

 the thigh. Garrod had already on these grounds divided a 

 Cuculine from a Centropine series ^. And in my memoir 

 upon the classification of this order or family I adopted the 

 facts given by Garrod (adding somewhat to them) in ray 

 definitions of the three groups into which I proposed — and 

 indeed still propose — to divide the existing Cuckoos. In 

 Centropus, &.C., the muscle-formula of the leg is the full 

 formula A B X Y with the ambiens. In Cuculus and its 

 allies the muscle-formula is reduced by the loss of B, the 

 accessory femoro-caudal muscle. It will be observed that 

 the loss of this muscle is coincident with the loss of the outer 

 band of the ventral feather-tracts. One cannot help thinking 

 that the apparent loss is a real loss in both cases, a reduction 

 from a more complicated state of affairs. In any case there 

 is no Cuckoo known with the formula A X Y which possesses 

 the outer band of the ventral feather-tract ; and, conversely, 

 no Cuckoo known which possesses that outer band that has 

 not also got the full muscular formula A B X Y. 



Hierococcya? proves to be no exception to this rule, at 

 present universal. The muscle-formula of the thigh is 

 A X Y with, of course, the ambiens muscle also. 



The third structural feature upon Avhicli I based my 

 attempted classification of the Cuculidte concerns the form 

 of the syrinx. This organ is developed along two lines in 

 this group of birds. In many forms the syrinx is apparently 

 of the most typical avian form, in which tlie intrinsic muscles 

 of the syrinx are attached to a bronchial semi-ring close to the 

 point at which the trachea divides into the two bronchi. 

 This form of syrinx is generally known as the tracheo- 

 bronchial, and is — as is well known — the most usual form 

 * Coll. Scientific Papers, ed. by W. A. Forbes, London, 1881, ji. 220. 



