OSTEOLOGY OF LAEIDiE. 597 



ulation lietween these two last vertebrro and the one just before them, producing a 

 Boraewhat moveable joint, never so firmly consolidated as are the other dorsal vertebrae 

 with each other. But for the fact that they are oostiferous, therefore, the two last 

 vertebrfB might be considered as a portion of the sacrum. 



On the first dorsal there commence abruptly prominent subrectangular spinous 

 processes, which are a distinguishing feature of this portion of the column. These 

 processes of any two contiguous vertebra' are in contact for their whole extent, and 

 more er less completely consolidated. Scleroskeletal tendons extend backward from 

 the posterior apices of eaeh of them. The transverse processes are all broad, thin, flat, 

 horizontal, stretching outward and a little backward, strengthened by a lirop, which 

 proceeds from the sides of the bodies of the vertebric to the apices of these processes. 

 Their apices bear the ordinary facet for the articnlat ion of the rib, and from each there 

 stretches backward an osseous tendon. 



The bodies of the vertebra^ are uot so deep vertically nor so compressed as usual. 

 Anteriorly, indeed, they are wider tban deep; their free ventral surface broad and 

 roughened, either with or without tubercles, as far as the fourth, for the attachment 

 of the longus colli. The other posterior vertebra' are thinner, being especially com- 

 pressed at their centres. 



Although the vertebriB of this region canuot be said to be anchylosed, except per- 

 haps in -^ery old birds, yet they enjoy but very little motion upon each other, par- 

 ticularly the more central ones. The first is usually moveable to a degree, while some 

 little motion is permitted between the sixth and seventh. 



Sacral ■S'ERTEBR.e. — It is difficult to ascertain the number of vertebrfe in the sac- 

 rum, but, as well as can be made out, the Slerniiiw have one less than the other sub- 

 families. Tlie elements of the sacrum are comiiletely consolidated into one piece, 

 together with the last two dorsal; so that it is ouly by counting the number of trans- 

 verse processes which stretch outward to abut agaiust the innominate bones that 

 their number can be estimated. The body of the sacrum is thickest in the middle, 

 taperini; somewhat toward both extremities; the tapering, however, of the anterior 

 extremity is only apparent, since it makes up by increased depth for decreased width. 

 The body is decidedly curved, giving a notable degree of antero-posterior concavity to 

 the dorsum of the pelvis. Anteriorly the iliac bones unite on the median line, and the 

 united spinous processes of the sacrum are completely anchylosed with them as well 

 as the transverse. About the middle of the sacrum the ele\ated longitudinal ridge 

 formed by the united spinous [irocesses disappears, and the median line of the bone is 

 smooth and flat. There are no signs of inferior or ventral spinous processes on any 

 part of the length of the sacrum. The transverse processes of the fir.st three vertebrae 

 are conspicuous, and project directly outward to be consolidated with the middle of 

 the under surface of the ilia ; the next three are short and inconspicuous, very little 

 more than ridges on the body of the sacrum. The seventh pair, however, suddenly 

 become the longest of all, running far outward, reaching even qnite to the margins of 

 the acetabula, and they are strengthened by a thin vertical plate of bone, which 

 stretches down from them to the dorsum of the ilia. The succeeding transverse pro- 

 cesses are well developed, projecting obliquely outward and backward to join the 

 margin of the ischia. 



Coccygeal vertebrje. — ^The coccyx has constantly eight segments. These are 

 chiefly noticeable for the length and width of their transverse processes. In Stercora- 

 riiis they are larger than elsewhere, being all of nearly the same length, whereas iu 

 other genera the anterior ones are more or less shortened, and do not reach their full 

 development until the fourth or fifth vertebra. These processes become very small on 

 the sixth, and are obsolete on the seventh. Superior spines are present, moderately 

 well developed, hut short. Ventral spines are wanting on the iirst three, but quite 

 largely developed on the last five vertebra?. Tliey are much the largest in Slercorarius, 

 and bifid at their extremity. 



The pygostyle is large, of an irregularly trihedral shape ; its superior margin convex, 

 its inferior a little concave; its base thickened for articulation with the seventh. Its 

 two superior angles are thin and rounded ; the inferior is prolonged into a thick, stout 

 nodulated apex. ■ 



EiBS. — The ribs are eight in number. Of these all are articulated with the spine, 

 there being none disconnected with it, as in some other genera of Xatatores. Six have 

 a sternal attachment as well as a spinal, while five possess retrocedent processes. The 

 first is an exceedingly slender elongated spiculum of bone, tapering to a very acute 

 apex, which is free. It extends to about opposite the process on the second rili. The 

 next five ribs have both vertebral and sternal portions movably articulated. Of these 

 the former are greatly the longest, and elongate rapidly with each successive rib. The 

 sternal portions are very much shorter, but also lengthen rapidly from before back- 

 ward. The splints which stretch backward and inward between one rib and another 

 are well developed. In the unexpanded thorax they reach quite across two intercostal 

 spaces. The " sacral ribs" are very long and extremely slender. Tho first articulates 



