OCR Text |
Show 1890.] ANATOMY OF PODICA SENEGALENSIS. 439 project freely as a vertical plate of bone between the two ilia. states that there is a ridge running as far as the end of the pelvis which marks the boundary between the postacetabular portion of the ilium from the ischium on each side ; I have already contrasted the pelvis oi Podica with that of the Rails by the absence in the former of such a well-marked ridge. In this particular therefore it appears that the Neotropical Heliornis has diverged less from the Rail-pattern than Podica has. It is evident, however, from Giebel's description that Podoa offers no very great differences from Podica, and that both these birds present a very much closer resemblance in the characters of the pelvis to the Rails than they do to the Grebes or Divers. Giebel thus describes the ribs in Heliornis:- " Podoa possesses eight pairs of ribs, and of these the first and second are false ribs, without uncinate processes, the following broad and flat, all bound by quite flat sternocostalia with the breast-bone, with slender uncinate processess, each reaching to the next rib, except on the two last. These latter are covered at their articulation by the pelvis." I have attempted to construct from this description a formula to compare with that of Heliornis, but I am not quite clear from the description whether a free cervical rib is present and whether any of the last ribs are lumbar. But apart from this it is clear that Podoa differs considerably from Podica, chiefly in the fact that there are no rudimentary floating ribs behind the last, which is attached to the sternum. The differences indeed between Podica and Podoa in these structures are (if the specimen studied by Giebel wras not in any way defective) if anything greater than the differences which distinguish either genus from the Grebe or Coot. The following table indicates some points of comparison, as to the number of vertebrae, ribs, & c , between Podica and some other birds :- Podiceps cornutus Podica senegalensis ... Heliornis surinamensis Uria troile Cervical vertebra?. 19 13 15 14 13 13 13 Dorsal vertebra? fused. 2-5 0 0 0 0 0 0 Ribs. r + R + 6 + 1 (2 lumbar) r 4- R + 7 + 1 (lumbar) r -f- R + 6 + 2 (3 lumbar) r+R + 8 r + E + 7 + 2(2 lumbar) r4-R+74-2(2 lumbar) r -f- R + 7 + 2 (3 lumbar) Uncinate processes. 2^-7 3-8 3-7 3-(i 2-9 2-8 2-8 30* |