002 DR. R. -W. SHUFELDT ON THE OSTEOLOGY OF THE [DfC. J, 



studies of the structure of the present genus. In T. alexavdri 

 we find that the hone has a round anterior margin witli complete 

 abortion of tlie manubrial process. Just witliin this line, tlie sternum 

 is much thickened, mounting up above in the median line into 

 quite a prominent pyramidal elevation. On either side of this a 

 circumscribed pit is found, while mesially, and directly behind it, is a 

 single pneumatic foramen. For the rest, the dorsal aspect of the 

 bone is smooth and generally concaved. 



The costal processes are conspicuous, being directed forwards and 

 outwards, and either costal border behind them supports five articu- 

 lations for the costal ribs. 



Plate LX. fig. 6 shows the wonderful depth of the sternal keel in 

 this unrivalled little prince of volants. In front it is fortified by a 

 thickened rib of bone, as in most carinate birds, while its convex 

 inferior margin is finished off with a rim, which, appreciably ])rojccts 

 beyond it all along its sides. 



The posterior sternal margin is entire, being convex outwards and 

 approximately a portion of an arc of a circle with a radius of 6 

 millimetres (2'4 nims. in the fig., it being x 4). 



Much stress has been laid upon this fact in comparing the Troclii- 

 liclce with the Swifts ; but a comparison of the figures will at ouce 

 show how essentially different these bones are. 



Turning now to the slwuldcr-girdle of Trochi/iis ale.vandri, we are 

 confronted with an exceedingly interesting structure and one which 

 markedly departs from these elements in ordinary birds. Of the 

 three bones the most striking difference is seen in the coracoid (Plate 

 LX. fig. 5). This element has a straight shaft with a very slightly 

 dilated sternal end, tlie whole being much compressed in the antero- 

 posterior direction. Just above its middle it is ])ierced by an ellip- 

 tical foramen with its long axis corresponding with the long axis of 

 tlie shaft ; immediately above this, again, we find a similar foramen 

 that represents the tenditial cinal in other birds, but here completely 

 surrounded by bone. The glenoid cavity is comparatively large and 

 projecting, \^hile the summit of the bene, when the arch is in situ, 

 points towards tlie median plane. 



Professor Owen's figure of T. pella referred to above shows very 

 well indeed the position of the furcula, when articulated as in life, 

 in the Hummers. Its seemingly high position is largely due, how- 

 ever, to the great depth of the carina in these birds. 



As for the bone itself, we find it assuming a form at the very limit 

 of tlie U-shaped variety. 



Its limbs are almost filamentous in character, and the hypo- 

 cleidium of rudimentary development only. 



Its heads are compressed from side to side, but very slightly enlarged, 

 and are quite shar}ily crooked downwards and backwards to have 

 their apices meet the scapulae. They rest against the coracoids on 

 the mesial side of the bridge that closes in the tendinal canal alluded 

 to above. 



A scapula contributes but a very small share of the articular surface 

 to the glenoid cavity — less than a fourth, I should judge. 



