SHUFELDT : OSTEOLOGY OF THE STEGANOPODES 



127 



keel of the sternum as described above. The upper free extremities of the clavicles are 

 drawn out, rounded, blunt-pointed and the apex of each one, when articulated in situ, 

 reaches back, on either side, to the antero-mesial angle of the corresponding scapula. 



A scapula is long, very narrow, rounded, and somewhat compressed in the ver- 

 tical direction. Its distal end onl}^ is blade-like, very shghtly expanded, and 

 obliquely truncated from a point within to the apex. - It articulates in the usual or- 

 nithic manner with the coracoid, and neither it nor the os furcula appear to be pneu- 

 matic, as is the coracoid. This latter bone of the shoulder-girdle has a broad, much 

 expanded sternal extremity, which supports a moderately prominent lateral coracoid 

 process. The entire length of the bone is greater than half the length of the humerus, 

 and its shaft is compressed in the oblique antero-posterior direction. Its head or 

 summit is tuberous, and also somewhat compressed in the same plane with the 

 shaft. The process for articulation with the os furcula is large, much flattened from 

 side to side, and low down in the deep tendinal groove it creates, we observe a 

 minute antero-posterior perforation of the bone. As usual, the coracoid and scapula 

 form a well defined glenoid cavity for articulation with the head of the humerus. An 

 OS liumero-scapulare is not found. 



Of the Appendicular Skeleton. The Pectoral Limb : Apart from the mere matter 

 of the difference in size, the bones composing the limbs in the skeletons of these two 

 species of Phaethon are in their corresponding characters almost exactly alike, and 

 these again are notably different from those same characters as we find them exem- 

 phfied in the limb-bones of the skeletons in other families of the Steganopodes. 

 These departures will be noted from time to time later on in this paper, after the 

 present account of the osteology of the Tropic Birds has been written. 



In the brief subjoined table some of the lengths of the bones are compared, the 

 measurements being given in centimeters and fractions. 



Table. 







Species. 





Measurements, taken from extreme distal points, 









and not on curved contour lines. 



P. flavirostris. 







P. sethereus. 



Length of humerus. 



8.4 







9.3 



Length of ulna. 



8.9 







9.7 



Length of carpo-metacarpiis. 



4.3 







4.8 



Length of proximal phalanx of index digit. 



2.5 







2.9 



Length of distal phalanx of index digit. 



2.4 







2.8 



Total length of pinion (articulated). 



8.8 







10. 1 



Length of femur. 



3.2 







3.7 



Length of tibio-tarsus. 



4.7 







5.3 



Length of tarso-metatarsus. 



23 







2.8 



Length of mid anterior toe. 



3.8 







4.2 



