44 AMKK/CAX X.rn-A\4L/S7\ [W.i.. XXXVIII. 



by the rrinatoritkr. I-'urthcr al.Mi- I shall refer t<. this matter 



The study of the patella in birds is a very interesting, not t.) 

 say, an important one, and, as has been noted abo\ e. as lon.-^ a^;-o 

 as 1884 the writer published an article in the J'rocct ch'iio-s of the 

 United States National Museum on the subject (\ ol. \TI, pp. 

 324-331) in which was figured the patellae of certain penguins, 

 mergansers, gannets, grebes, divers, fulmars, Hesperornis, crows 

 and cormorants ; and to that article the reader is referred for 

 information touching what has just been .said above. 



There can be no question about the existence of the patella in 

 the grebes, nor in Hesperornis, nor in the cormorants, but as I 

 have already shown, morphologists are not thoroughly agreed 

 upon the nature of the flake-like sesamoid found at the knee in 

 a loon, nor homologically speaking, its significance. Granted that 

 a large patella in the Urinatoridje has fused with the long cnemial 

 process of the tibio-tarsus, then it would hardly appear that the 

 small flake-like bone in the tendon of the extensor femoris muscle 

 should be considered a patella at all, although in the matter of 

 position it agrees with that sesamoid as it is found in all birds 

 that possess it. It would hardly seem reasonable that Urinator 

 had two patellae at either knee-joint, and such very dissimilar 

 ones. In my opinion the last word upon this subject remains yet 

 to be said. The embryology of the UrinatoridjE, as well as the 

 morphology of the structures involved in specimens of nestlings 

 and subadults of the species in all stages of their growth, requires 

 inve.stigating. 



In the Journal of Anatomy (London) (Vol. XXIV, January. 

 1890, and other volumes) I published a " Brief Summary of the 

 Prmcipal Osteological Characters of the Urinatorid^ " to which 

 I refer the reader for further details regarding the osteology of 

 the grebes and loons. 



It now remains for me to compare the principal osteological 

 characters of the loons and the grebes. These may be conven- 

 iently arranged for reference in the following manner : — 



