18!J9.] 



OSTEOLOGY OF THE PYGOPODES. 



1039 



The Tubinai'es and Alcidae both develop large cneinial processes, 

 which, as in the Pygopodes, project vertically beyond the femoral 

 articular surface. But these never attain the size of those of 

 the Pygopodes, and diifer, moreover, in form. In the Alcidse the 

 ento- and ectocnemial crests bear about equal shares in the 

 formation of the process, but the former starts suddenly from the 

 shaft just below the head of the tibia, in the Pygopodes it arises 

 near the middle of the shaft and more or less gradually increases 

 in size, and in the Tubinares it arises as in Alcidse, but imme- 

 diately expands into a more or less flabelliforra plate. 



Fig. 3. 



f.tr- 



Outer aspect of the pelvic limb of Podicipex cristafm, nestling. 

 p.t., proximal tarsal mass ; other letters as in figs. 1 & 2. 



About the exact homology of the great cnemial crest of the 

 Pygopodes there seems to be some doubt, even now. 



According to Shufeldt (18) it is to be regarded as repre- 

 senting the olecranon of the ulna, and both are to be treated 

 " as mere extensions of the shaft of the bones " to which they 

 belong. The cnemial crest, or " rotular process," is stated by 

 him to have a separate centre of ossification, separate from that 

 of the tibial epiphysis. The patella, which has been held by 



67* 



