520 KEPORT OF NATIONAL MUSEUM, 1888. 



The following table gives the result of the examination of thirty-one 

 sterna, although it should be said that in some cases one costal border 

 was wholly or partially lacking. Still as only one case occurs among 

 the entire sterna in which the number of ribs attached to each side 

 varied, the fact is comparatively unimportant. 



Sterna with six pairs of articular facets 1 



Sterna with seven pairs of articular facets 23 



Sterna with eight pairs of articular facets 6 



Sterna with seven facets on one side and eight on the other 1 



Total number of sterna examined 31 



Of the sterna with eight pairs of articular facets two had evidently 

 borne a hsemapophysis attached to the second, posterior cervical rib. 

 While the coracoid presents considerable variety in the amount of de- 

 velopment of the epicoracoid as well as in the shape and extent of the 

 sternal articular surface, it is always unmistakable in its general con- 

 tour, and the same may be said of nearly all the bones of the Great 

 Auk. 



The greater number of humeri are from 103 to 108 ^^ in length, and 

 it is interesting to note that the mean of three hundred humeri agrees 

 very nicely with these figures, being 105.75 ™"^. 



This bone, perhaps the most characteristic of the entire skeleton, 

 seems to vary less in its proportions than any of the other long bones, 

 not presenting such perceptible differences in diameter as are found in 

 either the femur or tibia. 



It is a little singular that the greatest amount of linear variation — 

 taking into consideration the length of the bone — should be found in the 

 femur, while it also shows very considerable differences of proportion, 

 some femora being much more slender than others of the same length, 

 the longest not always being the strongest. 



The same differences of length and proportions found in the femur 

 obtain to a lesser degree in the tibia, and also in the tarsus. This last 

 bone occasionally develops a small tubercle on the postero-internal edge, 

 about where the first metatarsal arises in four-toed birds, a peculiarity 

 noticed by Professor Milne. 



Thirteen out of one hundred and forty- two tarsi have this tubercle, 

 and although it ordinarily appears to form an integral part of the tarsus 

 there are some specimens which indicate that in young birds it may 

 have been free, so that the tubercle probably represents a rudimentary 

 first metatarsal. 



This and the frequent presence of an extra pair of ribs would seem to 

 be reversionary characters, hinting at some ancestral form with more 

 digits and more ribs than the Great Auk. 



The measurements of so considerable a number of bones from oppo- 

 site sides may be looked upon as throwing some light on the question 

 of correspondence in size between bones from the right and left sides, 



