1888.] PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 307 



to lodge an air-sac, but the lack of fresh material prevents me from 

 speaking positively upon this point. 



Other pneumatic holes occur at the distal end of ulna upon all sides, 

 except the outer one. The olecranon, though large and rather tuberous, 

 would not particularly attract our attention. 



A distinct canal upon the outer aspect of the distal end of the shaft 

 for the passage of the tendons characterizes this bone. The articular 

 surface shows nothing of special interest. 



As usual, the carpal segments are but two in number — a radiale and 

 an ulnare. They present the forms and facets common to these bones 

 generally. Both are pneumatic and have large apertures for the admis- 

 sion of air to their hollow interiors. 



The carpo metacarpus also presents a number of these foramina at 

 either of its extremities; the principal one, however, is found just 

 below the trochlear surface formed by os magnum upon the anconal 

 side of the bone. A notable process occurs immediately below it, and 

 another group of these air-holes to its outer aspect near the short atid 

 inconspicuous first metacarpal. 



The main shaft is straight and of good caliber; it is longitudinally 

 grooved nearly its entire length on the palmar side for a tendon going 

 to the fingers. This is best marked upon the distal moiety of the bone. 

 The metacarpal of middle digit is also straight for the major extent of 

 its continuity; its extremities becoming enlarged in order to allow it to 

 make the usual connections with index metacarpal. It is rather slen- 

 der and develops no special processes, as it sometimes does in other 

 representatives of the class. 



The expanded portion of the proximal joint of index digit is not per- 

 forated, not even by the numerous pneumatic foramina which are irreg- 

 ularly scattered over its surface. Below it is produced as a notable 



Fig. 38. Eight metacarpus of Sula bassana; anconal aspect ; life size. By the author, from the same 



specimen as shown in Fig. 24. 



process, and a process that is seen in some of the extinct birds, as in 

 Ichthyornis, for instance. The shaft of this phalanx is broad and flat 

 anteriorly, and perfectly straight from above downward. 



Equal to half the length of carpo- metacarpus, the distal phalanx of 

 index digit is of a trihedral form, with an extensive excavation at the 

 posterior aspect of its proximal end, which is continued in a lesser de- 

 gree the entire length of the bone. It bears no claw below, but is fin- 

 ished off by a distinct little process. 



Pollex phalanx has very much the same form as the one just described, 



