148 



MEMOIRS OF THE CARNEGIE MUSEUM 



Where remarkable differences do come in, is in the relative lengths of these bones 

 when we come to compare them in one species with the corresponding bone in an- 

 other. In speaking of Sula bassana, I said above that its humerus was longer than 

 the radius or ulna ; now this is not the case in other species of Gannets, as the sub- 

 joined table will plainly show. 



MEASUREMENTS IN CENTIMETERS AND FRACTIONS. 



Of the Pelvic Limb. In comparison with the general size of Sula bassana the 

 lower extremity is very short/though the bones composing its skeleton are none the 

 less strong in consequence. In the femur we find the axis of the head and neck 

 making an angle with the longitudinal axis of the shaft. The head is quite dis- 

 tinct, globular, and, as usual, excavated on top. Its surface is continual with the 

 broad articular surface which occupies the entire summit of the bone. ISTo trochan- 

 terian ridge rises above this latter, and, indeed, this character of the femur is but 

 poorly developed. 



A pneumatic foramen is always seen at its most common site, on the anterior 

 aspect, just below the superior articular surface. 



The shaft is cylindrical, roughened in some places by lines and diffuse tuberosi- 

 ties for muscular attachment, and is bent slightly to the front and somewhat to the 

 inner side. At its distal extremity the condyles are fashioned after the usual pattern 

 among birds, but all their characters in Sula present a sort of lack of strong devel- 

 opment. The fibular cleft is but faintly marked, the intercondyloid notch or fossa 

 is shallow, and the ridges in front much rounded and inconspicuous. 



Something of the same condition is extended to the proximal end of the tibio- 

 tarsus of the leg, though not to such a marked degree. Here the cnemial process rises 

 but slightly above the articular summit of the bone, and the pro- and ecto-cnemial 

 ridges which descend below it soon merge into the shaft, and are, at the best not 

 very prominently developed. 



The shaft of this bone is straight and smooth and somewhat compressed through- 

 out from before backward. It offers a long ridge to the fibula and is broad across 

 where it is found. The distal extremity of the bone evinces more character than 



