694 SHUFELDT—OSTEOLOGY OF THE STRIGES. [Dec. 7, 
Owl now under consideration, with the exception of a few faint 
lines indicating the original individuality of the vertebrze, these 
bones are thoroughly anchylosed together and to the ossa innomi- 
nata. From inspection of this compound bone in immature birds 
we find the usual number of sacral vertebree composing the sacrum 
to be thirteen. The anterior face of the first possesses all the ne- 
cessary elements for articulation with the last dorsal. The neural 
spine has a thickened crest that soon meets the ilia on either side; 
its anterior edge is thin, and gives attachment below to the inter- 
spinous ligament. The neural canal is circular and the prezyga- 
pophyses well marked. ‘The articular facet of the centrum is in 
the vertical plane, with its curvatures similar to those ascribed to 
the anterior facet on the centra of the dorsals. | The neural spines 
are broad and the transverse processes are strong and raised, with 
their enlarged extremities expanded upon and firmly united 
with the iliac bones. There is but one pair of sacral ribs, and they 
are free ones. Long and slender, they articulate with the first 
vertebra in the usual manner, but the relation is much more inti- 
mate, as they touch the diapophyses for some little distance 
beyond the tubercula toward the capitula. The lower extremities 
of these ribsare terminated by little roundish knobs, which articu- 
late with the corresponding sternal rib on either side, described 
above as being inserted in the posterior border of the fifth sternal 
rib. Viewing the bone dorsal-wise, it is to be seen that the thick- 
ened crest of the neural spine of the first vertebra protrudes from 
the angle made by the ilia meeting it anteriorly to a greater or less 
distance. This broad and compressed crest, then continued back- 
ward, is firmly wedged between the ilia until we pass the third ver- 
tebra; at this point the ilia diverge from each other to another 
point just anterior to the acetabula, then converge, terminating in 
the posterior sacro-iliac border, within five or six millimetres of 
each other. The sacrum completely fills in the lozenge-shaped 
space thus formed from the third vertebra—first, by continued 
broadening and compression of the neural spine, that soon becomes 
one with the others of the series; and secondly, by the expanded 
extremities of the di- and parapophyses, the processes themselves 
also taking due part. The integrity of the surface is unbroken, 
save posteriorly, where a few pairs of foramina exist among the ex- 
panded transverse processes, increasing in size from before back- 
ward. Anterior to a line joining the acetabula the surface is in the 
