78 



ANATOMY OF VERTEBRATES. 



groove commencing near the lower end of the fore part of the 

 shaft leads, deepening, toward the intercondyloid space : it is 

 bridged over by a strong ligament, which becomes ossified in 

 most birds : Parrots, Hornbills, and existing Ciirsores are ex- 

 ceptions. The position — median or submedian and direction — 

 straight or oblique — of the precondylar groove, the presence and 

 direction — transverse or oblique — of its bony bridge, the re- 

 lative breadths, anteroposterior and transverse, of the distal end, 

 the relative size of the intercondyloid space to the anterior parts 

 of condyles, — help in the determination of bird-affinities, when 

 they have to be deduced from a fossil tibia.* The distal condyles 

 commencing behind as ridges bounding an articular surface con- 



34 



Pelvis and bones of the leg, Loon {Colynibus). 



cave across, increase in breadth and convexity as they curve to 

 their anterior ends : these are more prominent than their posterior 

 ridged beginnings, but in different degrees in different birds ; 

 and the inner condyle is usually the most prominent anteriorly : 



' Sec X1X-. p. 204, pi. 3, for the illustration and application of the characters of 

 the tibia in the determination of the affinities of birds indicated by that bone fossil. 



