100 ODOXTORNITHES. 



swimming- birds, and in their individual proportions remind one of the toe 

 bones of the Penguins. 



The Outer, or Fourth, Digit. (Plates XVIII and XX.) 

 In describing the phalanges of the feet, it will be convenient to begin 

 with the outer, or main, digit. This was supported by the large distal 

 articulation of the tarso-metatarsal bone, and its general direction was 

 forward, and somewhat outward, nearly in the same plane with the axes of 

 this bone and the tibia. 



The first phalanx (Plate XVIII, figure 1) is short and stout, and 

 somewhat compressed transversely, at its proximal extremity. This end 

 has two deeply concave articular facets for union with the condyles of the 

 fourth metatarsal. Of these facets, the inner is larger than the outer, and 

 the articular surface, as a whole, shows an approach to the peculiar joint 

 structure seen in the more distal articulations of the foot. The shaft of 

 this bone is rounded on its dorsal surface, somewhat flattened on the 

 external side, and deeply excavated on the outer inferior margin, a 

 character seen also in the succeeding phalanges. 



The distal end of this phalanx is sub-triangular in outline, and 

 entirely covered by the articular surface. The latter consists of a semi- 

 circular, slightly convex, articular facet, which occupies the inner two-thirds 

 of the extremity, while the rest consists of a prominent rounded peg, or 

 tubercle, projecting considerably beyond the remaining surface. This 

 process fits into a corresponding cavity in the proximal end of the succeed- 

 ing- phalanx. The more flattened surface, which partially surrounds this 

 peg, meets a similar surface on the inner side of the same phalanx. This 

 peculiar articulation necessitates rotation (feathering) with flexion, and 

 greatly increases the strength of the joints. This crescent-peg- joint, more 

 or less modified, is characteristic of all the principal phalanges of 

 Hesperomis, and somewhat the same structure is seen in the genus Podiceps. 



The second phalanx (Plate XVIII, figure 2) of the fourth digit 

 resembles the first, but is smaller in all its proportions, and considerably 



