902 DR. R. W. SHUFELDT ON THE OSTEOLOGY OF THE [Dt'C. 1, 



studios of the structure of tlie present genus. In T. alexandri 

 we find tliat the bone has a round anteiior margin with complete 

 abortion of the manubrial process. Just within this line, the sternum 

 is much thickened, mounting up above in tiie 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. 



Tiie 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 projects 

 beyond it all along its sides. 



Tiie 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 x4). 



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

 lidcB with the Swifts; but a comparison of the figures will at once 

 siiow how essentially different these bones are. 



Turning now to the sliovldcr-yirdle of Trochilus alexandri, we are 

 confronted v\ith 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). Tiiis 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 pierced by an ellip- 

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

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

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

 surrounded by bone. The glenoid cavity is comparatively large and 

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

 points towards the median plane. 



Professor Owen's figure of T. yella referred to above shows verv 

 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 tliese birds. 



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

 of tiie 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 sharjily crooked downwards and backwards to have 

 then- 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. 



