1040 MB. W. p. PTCRAFT ON THE [DeC. 19, 



Vicq-d'Azyi (20), Owen (13), and others to be the bomologue of 

 the olecranon, is considered by Shufeldt as a sesamoid only. 



Prof. D'Arcy Thompson (19) sees, apparently, like Selenka (15) 

 and Flourens," in the cnemial crest ot the Grebes and Divers 

 nothing more than " the npper extremity of the tibia." 



In a preparation in our Museum Collection, of the pelvic limb 

 of a nestling Grebe, the cnemial crest forms a part of the tibial 

 epiphysis in which a centre of ossification is just making its 

 appearance (fig. 3, p. 1039). From this it would appear that the 

 process in question is really only a greatly elongated epiphysis. 



The Jihula in the Colymbi extends downwards to the level of 

 the superior border of the extensor bridge ; it terminates in the 

 Podicipides near the distal g of the tibio-tarsus. 



Ihe patella in the Grebe is a very large, laterally compressed 

 pyramidal bone, the apex projecting above the level of the cnemial 

 process, whilst its inner surface is more or less closely applied to 

 the outer border of this process. Its base forms a longitudinally 

 elongated glenoid surface for articulation with the femur. 



In all the skeletons of Colymbi in the Museum Collection, 

 unfortunately, the patella is missing. According to Shufeldt (18) 

 and others it is, however, represented by a small flake-like bone. 



Prof. D'Arcy Thompson (19) holds that the patella proper of 

 the Divers has fused with the cnemial process, and that the small 

 patelliform plate is to be regarded as a sesamoid, and not ns the 

 homologue of the free patella found in Podicipes, Hesperornis, 

 aud other forms. This is a point which could probably be settled 

 by an examination of nestlings or embryos. 



Amongst the Alcidaj, e. g. Uria alle, the patella is more or 

 less quadrate in form, and articulates by the lower half of its 

 anterior surface with the apex of the cnemial process, this being 

 very much less developed than that of the Grebe and Diver. 

 Thus, the upper half of this border serves as a further extension 

 dorsad of the process itself. From this it will be remarked that 

 the position, size, and form of the patella, and the develop- 

 ment of the cnemial process, in the Alcidse is distinctly different 

 from that of the Colymbi, as also, it will be remembered, is the 

 form of the pelvis. 



In all these particulars it will be noticed that, though there is 

 a tendency in the Alcidie to modification along the same lines, — 

 to a convergence of characters, due to similar methods of progression, 

 resulting in a similar upright carriage when on land, — the 

 Alcidae are less specialized than the Colymbidae, which possibly 

 had its origin in that of the stock of the Cretaceous Resperomis. 

 The pelvic girdle and limb, in common with the rest of the 

 skeleton, of this bird, ax-e, as is well-known, almost indistinguishable 

 from those of the modern Colymbi. Indeed, when we eliminate 

 the presence of teeth, the Ratite steimum, vestigial \\ing, and 

 complete ilio-ischiadic fissure, the only points of difference appear 

 to be such as serve to distinguish species one from another. 



