98 BULLETIN UNITED STATES GEOLOGICAL SURVEY. \Yol.\I. 



and third the largest. Their anterior and posterior borders are concave, 

 allowing, when articulated, spindle-shaped apertures to exist among 

 them, while their summits are produced backwards and forwards, thick- 

 ened, and wedged into each other. This wedging is performed in the 

 following manner : The posterior extremity of the crest forming the sum- 

 mit of the neural spine of the first dorsal divides and receives the an- 

 terior extremity of the crest of the second. This same arrangement ex- 

 ists between the second and third, and at the summit between the third 

 and fourth, but the fourth immediately below the junction also divides 

 for a little distance and receives the edge of the posterior rim of the 

 third, just beneath the union of the crests. This latter method of join- 

 ing is feebly attempted between the fourth and last. (See PI. I.) The 

 neural canal is nearly cylindrical in the dorsal region, its calibre being 

 less at the sacral extremity, and rather compressed from side to side, as 

 are the centra as we apjjroach that end, each one being a little more so 

 than its neighbor beyond. Viewing these five vertebrce from above in 

 the articulated slceleton, we observe the spinous crest already described ; 

 we are struck with the regularity with which the postzygapophyses over- 

 lap and adjust themselves to the prezygapophyses from before back- 

 wards, like the scales in some fishes, the facets of the former facing 

 downwards and outwards, the opposed surfaces of the latter facing up- 

 wards and inwards. The neurapophyses are horizontally compressed 

 and rather broad ; the diapophyses jut from them at right angles from 

 points about their middles. There is an inclination for the latter to 

 be directed slightly backwards as we near the sacrum. The diapophy- 

 sis of the first dorsal is the shortest and stoutest, that of the last the most 

 delicately constructed. Superiorly, these processes supx)ort metapophy- 

 sial ridges at their extreme outer borders. These ridges on the diapophy- 

 ses of the first dorsal are the largest, rounded at both ends, extending 

 a little both backwards and forwards, but far from touching the ridge 

 either in front or behind them. The metapophysials of the last dorsal 

 are smaller, sharp, styliform, and project only forwards, though they 

 do not by any means touch the diapophyses in fi-ont of them. On 

 the intermediate vertebra they change gradually between these two 

 extremes, but in no instance meet the diapophyses of the vertebra be- 

 fore or behind them, and thus constitute an additional aid to the rigid- 

 ity of the back, as it does in other species of this family and in many 

 other birds. The centra increase in depth beneath the neural canal the 

 nearer they are to the sacrum. In the first dorsal the body measures 

 about one millimetre, the vertical diameter of the canal being three 5 in 

 the last dorsal it equals the diameter of the canal. The interarticular 

 facets are in the vertical plane, with their concavities and convexities op- 

 posed to each other, as they were described when speaking of the last cer- 

 vical vertebrae. The bodies are about of a length, constricted at their mid- 

 dles and expanding towards their extremities. The first two dorsals each 

 bear in the median line, beneath, an hypapophysial process of consider- 



