648 



DR. P. CHALMERS MITCHELL ON Till) 



[Dec. 17. 



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

 may be taken as evidence that in Eurypyga the iliac division is in 

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

 or absent. In Psophia (text-fig. 79, ( CA UD. )-IL.-FKM. ) it is present 

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

 feneration in the form of a large tendinous area nearly in tbe middle 

 of the muscle (text-fig. 80, (CAUD.)-IL.-FEM.) ; and 'Beddard states 



Text-fig. 80. 



[CAUD)-/LFfH 



CAUD-/L-FLFX 



ISC-FLEX. 

 PUB-/SC-FEM 



Thigh -muscles of Arami's scolopaceus ; right thigh, external view. 

 Lettering as in text-figure 79. 



that a similar condition exists in Cariama, a bird in which Grarrod 

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

 as disappearing. It is absent in Rhinoclielus. The division of tbe 

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

 present in the Rallidae and Heliornithida; 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 

 Rhinochetus. It is absent in the Aramina?, Psophiinae, Dicho- 

 lophida?, 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 Ballidae and by some Cranes, these 

 being diastataxic forms, but also by the eutaxic Heliornithida?; a 



