648 



DE. P. CHALMERS MITCHELL ON THE 



[Dee. 17, 



(accessory) was absent on both sides, and such individual variation 

 may be taken as evidence that in Eu7'ypyga the ihac division is in 

 process of disappearing. In the genus Balearica it may be present 

 or absent. In Psopliia (text-fig. 79, ( CA UD.yiL.-FEM.) it is present 

 and normal. In Aramus and in Otis it is present, but shows de- 

 generation in the form of a large tendinous area nearly in the middle 

 of themuscle (text-fig. SO, {OAUD.)-IL.-FEM.); and Beddard states 



Text-fig. 80. 



CAUD-/L-FL£X 



ISC-FLEX. 

 PUB-ISC-FEM 



Thigh -muscles of ^ramws scofojsaceMS ; right thigh, external view. 

 Lettering as in text-figure 79. 



that a similar condition exists in Oariama, a bird in which Garrod 

 found the muscle absent and in which therefore it must be taken 

 as disappearing. It is absent in Bhinochetus. The division of the 

 muscle with caudal origin (femoro-caudal)is, as I have mentioned, 

 present in the Eallidse and Heliornithidse and in some Cranes. 

 It is absent in the genus Balearica, and, according to Beddard, in 

 Grus leucogeranos. It is present, although small, in Eurypyga and 

 Bhinochetus, It is absent in the Araminse, Psophiinae, Dicho- 

 lophidae, and Otididae. It is plain that a tendency to apocentric 

 modification, consisting of reduction or disappearance of one or 

 of both divisions of this muscle, is a character of the Gruiform 

 assemblage, and the incoherent nature of the group is shown by 

 the chaotic incidence of the apocentricities. The archecentric 

 condition is shown by the Eallidse and by some Cranes, these 

 being diastataxic forms, but also by the eutaxic Heliornithidse ; a 



